I've been thinking about a character with a multiple personality disorder. It would be 6 personalities. Same stats for all 6 personalities. The personality would change randomly after every long rest. Each personality would also have a trigger that would bring it forward. Each personality would use the same stats. With every personality switch after a long rest roll to see how much information was passed along. The triggered switches get immediate knowledge of the situation at hand but nothing beyond the immediate situation. At the end of the trigger event I would roll to see what the character knows about events outside of the trigger event.

I'm thinking one personality would be an undead warlock, one would be a hexblade warlock, one would be a bard, one would be a barbarian, one would be a psi-fighter and one would be a rogue. Basically looking for 3 optimally constructed personalities and 3 sub-optimally constructed personalities. Obviously the classes for each personality could be assigned as desired.

That means potentially pacts with 2 different patrons and the need for a bunch of weapons on hand.

The active personality at the time of each level up chooses the asi or feat but each personality chooses their own class progression. Multiclassing would be restricted to 4 level chunks. Classes with access to extra asi's would be restricted to feats at those levels as all the characters would be required to use the same attributes scores.

I think the triggers for each personality would be assigned randomly based on aspects of the event that caused the personality split. The base personality would have to be chosen and each character's hp would be based on the base personality's progression. The race options and background options would be the same for every personality. 

The personalities would share the same race and background options and their 4th, 8th, 12th, 16th and 19th asi's would be the same.

Would this work? Or is too jack of all trades (an excuse to play 6 different classes)?

I built a similar character for a campaign, and while it was a lot of fun for me, I've decided that it is a horrible idea for a group game.

It's twice the work for the DM, 6 times the work for you, and none of the other players are going to be paying enough attention to appreciate the internal gymnastics. It will simply come across as being erratic and bad roleplay. It also has a very high risk of stealing the spotlight from the other players.

I would only recommend this kind of character if you are (A) playing with people who know you very well, and (B) if you are actively involved in theater, either as a professional, or an enthusiast. It is a choice that requires both the trust of your table, and the expressive chops to make each personality uniquely vibrant. Subtlety gets lost in the noise.

The best platform for this kind of character is short-novel grade PbP where you can do internal monologues and control your personal narrative in meaningful chunks.

This sounds very complicated  for both you and your DM and very likely to be confusing for the others in your party. Even if you explain the multiple personalities to the other players, their characters won't necessarily know or understand what is happening.  I can, however, understand how this idea would appeal from a role play perspective, so with that in mind, you might want to consider one of the following races as a simplified take on the concept.

The first one that occurred to me was an Eladrin.  The description for this subrace specifically states that  "Some eladrin remain associated with a particular season for their entire lives, whereas other eladrin transform, adopting characteristics of a new season."  This would give you four different personalities (one for each season) with the option of changing every long rest.  From there, you could talk with your DM about adding the Triggers mentioned in your post.  (I did something very similar to this with a significant NPC I made to introduce my players to the Feywild and the only negative comments were that they all preferred to avoid her winter aspect after the first time.)  

Another possibility, if your DM allows, might be to make a Changeling character from Eberron: Rising from the Last War.  These are natural shapeshifters who adopt Masks or personas for a variety of  purposes.  You could then have a different appearance for each personality you wanted to develop.  If you combine this with the Bard character class, you could easily have each personality/mask associated with a different skill set, such as one for martial combat, one for healing /divine casting, one for arcane casting, and one for subterfuge.  That would give you a lot of versatility without needing to multi-class, since bards already get Jack of All Trades, Expertise, and Magical Secrets.  Just pick the college that best supports what you want most to emphasize.  As for what your character thinks or remembers at any given instant or when using any particular mask, that should be a matter of role play and entirely within your control.  

I hope this helps and that whatever you create you and your group have many wonderful adventures.  

First thing that comes to mind is that you are dangerously close to making mock of a serious mental disorder.  There are people who may not like that.

Second is that you should not gain a benefit from something that ought to be a detriment. 

Third, you will be using a lot of time.  The other players may not be all that pleased if they have to wait while you decide what you want to be, what triggers you this time, what you remember, or what you have done.

Feel free to roleplay to your hearts content, but do not mess with skills, feats, stats, classes, proficiencies, or anything else.  If your Warlock thinks they are a Bard, all well and good.  This should not change your Performance skill in any way.  They still don't get a benefit if they think they are a Barbarian and take their armor off.  They get no extra dice if they try to sneak attack because they think they are a Rogue.  They can't take Elven Accuracy because they think they are an Elf.

A Warlock doesn't get to have two Patrons at the same time.  No matter what they might think or how they act.  The best that can be hoped for is that the Patron won't become offended in some way.  Play a Warlock, grab Mask Of A Thousand Faces and have a different appearance for each personality.  You appear to like Warlocks, they came up in your list twice..

Different personalities often fight with each-other.  They struggle for control.  They may have different Alignments and take actions when they are in charge to harm the other personae.  Your Rogue may decide to sabotage your Barbarian, steal from the party and decide not to tell them.  Then the Barbarian may become enraged and attack the party when accused of theft.  A Warlock has a Patron who may whisper in their minds.  That's just perfect for creating chaos.  Different personae communicate with each-other.  Which of the voices in your head is actually real?

Bad idea all around.  Roleplay as you wish, as long as everyone at the table is having fun you may do as you like.  As always.

Rather than playing with mental illness and having too much complexity, you could consider having a possession. A well mannered studious mage that every so often loses control to the demon inside, at which point he becomes a raging barbarian. Two classes but one set of stats. Both see through the characters eyes, even when not in control, so both have the same knowledge and know the same people.

As someone who can speak with authority on the matter:

Don't.

It is very difficult to play Dissociative Identity Disorder (formerly known as Multiple Personality Disorder) with any level of respect, and trying to somehow tie it into game mechanics of any kind will just cause a headache for you, the DM, and make the roleplay increasingly difficult with the other players. 

but the biggest concern is the fact that it is a serious disorder. And we don't need people trying to play it off as some kind of joke or parody, or do it poorly any more than we need people trying to play an autistic savant based on terrible stereotypes from media.

Quote from DevanAvalon >>

As someone who can speak with authority on the matter:

 

Don't.

 

It is very difficult to play Dissociative Identity Disorder (formerly known as Multiple Personality Disorder) with any level of respect, and trying to somehow tie it into game mechanics of any kind will just cause a headache for you, the DM, and make the roleplay increasingly difficult with the other players. 

but the biggest concern is the fact that it is a serious disorder. And we don't need people trying to play it off as some kind of joke or parody, or do it poorly any more than we need people trying to play an autistic savant based on terrible stereotypes from media.

I came here to say ^ this. 
I was very personally close with someone struggling with Dissociative Identity Disorder - back when it was still called "MPD" - it was a very painful struggle to watch a loved one grapple with, and not be able to do much of anything to help (at the time). There was eventually a tragedy that ended that time in my life. 

I am also neurodiverse, but in a different way. Our lives and our struggles are not costumes to play with nor can be reduced to homebrew game mechanics. 

That having been said - the only person who can decide what you actually end up doing is you. If you truly want to roleplay a neurodiverse character, I would suggest looking less at game mechanics, and more at character build. And do a little bit more to learn what you're about - from actual people living real lives with mental illness. The impact of living with something like DID can vary widely depending on other factors like race, class, religion, and access to mental health care & other social support systems. 

Basically... these are the kinds of things that would show up better in your character's background, bonds, traits, weaknesses, or even maybe a feat. You'd want to take time to think about how your character experiences DID - when they dissociate, is it scary? do they experience secondary symptoms like fugue state, brain fog, migraines, depression, or anxiety? Did they have access to health care as a child? as a teen? as a young adult? How has this facet of their life impacted their relationships, positive or negative or both? How are their parents interacting with a neurodiverse child? How about siblings? Neighbors? Friends? What are the kinds of things that can trigger a dissociative episode IRL? What triggers could you adapt faithfully in a fantasy setting? What efforts will you make to roleplay this condition accurately to the best of your ability? 

Most of all... a DID person is one, same, person - no matter what is going on in their neurophysical experiences. When a diabetic experiences a sugar high or low, they don't stop being a baker and start being a plumber. When you catch a cold, even if you are grumpy or uncomfortable, or even delirious with a fever - you are still YOU. Your reactions and symptoms and affectation and ability to have a conversation or concentrate on reading a book are impacted by your physical state, yes.... but you don't gain or lose whole skill sets. I hope that you understand my meaning here. Someone who experiences DID in their life, no matter what identity or personality or other symptoms they might be dealing with at any given time.... that's still a part of who they are as a person. 

However, if what you actually want to work with is a character that is trying to manage multiple, distinct, skill sets... (btw - 6 is waaaay too many to juggle)... you can always (1) just multiclass and be that jack of all trades, (2) have a curse, (3) be possessed, (4) have been in an accident with mild magic, (5) be a person enthusiastic about living life, but who hasn't yet found the thing that really "clicks" and so they've been moving from career to career in search of "The Thing For Me" .... Or even, when you were a child, a fae passing by asked what you wanted to be when you grew up, and being just a kid, you answered "a fighter - no, a wizard!" and the mischievous being of magic thought it would be amusing to "bless" you with ending up as both!  

There are tons and tons of possible roleplaying hooks that would cause a character to end up with distinct skill sets - especially in a reality with magic, literal blessings and curses, fey folk, etc. If it's mostly the mechanics that you want to play around with, sit down with your DM to work out a setting-appropriate reason a person might be walking around sometimes one thing and sometimes a different thing. Think less "serious, real, disorder" and more "Dr Jekyll and Mr Hyde" and bring on the experimental magical potions!!

I agree with the others that playing multiples is fun for you and crap for the rest of the party.  

Also, in real life people with atypical minds tend to get screwed over by everyone - they are the victims not the predators.  This is despite the horrible rep they get in media where they are usually the villains.   How are you going to deal with a villain that realizes what you are and recruits one of your personalities to his side?

Ever see Memento ?   That character gets screwed over by everyone.   His landlord rents him multiple rooms.   His friend uses him to murder innocent people.  His 'girlfriend' abuses the crap out of him.  But still he somehow is portrayed as the scary guy.

Quote from Mog_Dracov >>

 

Ever see Memento ?   That character gets screwed over by everyone.   His landlord rents him multiple rooms.   His friend uses him to murder innocent people.  His 'girlfriend' abuses the crap out of him.  But still he somehow is portrayed as the scary guy.

Without spoiling the ending, it does justify the scary guy vibe. 

I think you can absolutely pull of a simplified version of this, but the current implementation seems way too complex - for you, for your DM, and for the rest of the players. Way too much of the game's focus needs to be dedicated to you in order to make it work.

Eladrins are a good example of how this might work well. They can change seasons at the end of their long rest, and their seasons often correlate with mood. That's a simple way to change up your personality a bit from day to day without resorting to this huge persona shift. Best of all, it comes with a clean visual cue for the rest of the party, which makes the mechanic much more digestible for everyone involved.

Meanwhile, any class with prepared spells can let you do fairly drastic mechanical shifts. You could have a bunch of preset spell lists depending on which form you take. An Eladrin druid, for example, might have more fire-themed spells in their Summer Form, vs cold-themed spells in their Winter form. I think it'd be fair to work with your DM to have a rotating cantrip or some other small mechanical piece like that, but anything beyond that is just a huge hassle.

You might be able to do a little bit more if you only swap between two personalities. A two-pact warlock, for example, seems like it could be an interesting idea without completely taking over the game. Its a much cleaner and more interesting narrative.

Oh - FYI - if you have access to Baldur's Gate: Descent into Avernus (or just access to Google) 
That sourcebook has a background called "Faceless" - maybe check that out? 

I hope some of these responses have been helpful for you in some way!! 

I think it's perfectly possible to do somerhing like this without being insensitive about actual disorders. Just explain the characters condition has some kind of magical cause or similar so you don't act as if your character has a condition that reflects the struggles of real people.

I have actually tried something similar on a character.. It wasn't really a condition for my character, it was more a way for them to deal with being a mindreader and being exposed to a bunch of people's memories. So while I think it's possible to do it.. don't think it's a good idea either.. It ends up being a super complicated affair for you, and the rest of the party will only have time to engage with the very surface level of each personality which will actually make your character seem less interesting in the end.

If you really wanna go with this kind of approach, I recommend simply sticking to 2 personalities with clear and fun distinctions.

I think this is a terrible idea. First and most important, you are making fun out of a serious illness, it is simply disrespectful to the people struggling with it and you don’t know if one of your fellow players doesn’t have someone in their family struggling with it, you can’t expect them to just tell you because this isn’t something people are comfortable sharing. Trying to use it in order to be allowed to play several different classes at once is just insensitive and not something you should strive for. Second, this isn’t even how a multiple personality disorder works, this looks an impression of what multiple personality disorder is by a person who only knows it from jokes about madmen or stupid comedy movies. Thinking that you are a warlock does not grant you any spells. Finally, this looks like you are trying to make a character that can do everything, it’s going to be annoying to other players. 

Why would you even want to do something like this? If you want to be good at everything, just play a bard and maybe multiclass, don’t use a serious real life illness with very serious real life consequences for your personal amusement.

This is also at its base just a game, where you are playing someone that is not you. I agree it's something that is super tedious to try to having your game (one of my players is essentially doing this as a result of madness directly from the Demogorgon, and switches personalities of past party members who died whenever he rages). 

It's only a joke or parody if the player is making it as such. I dont see any issue with trying to add this sort of extra roleplay challenge if done seriously.

 My recommendation for OP is to not do it with multiple classes, but to just make it a flavor thing or else itll get WAY too much to handle with switching classes. 

But the OP seems to have largely shaped this character around the multiple classes.

To assess with a broad brush, and ignoring the clear "wouldn't be neat if I had multiple personalities" rather than "I think it would be compelling in our game to explore this pathology" in the characters conception, I think it pulls a little too much focus on this character if at every encounter this one player has to ask "who am I now?" and the rest of the party has to wait while the player and DM play the mental health mini game the player imposed on the group during character generation.

I've done things like this but without evoking mental health pathologies.  You can have characters with "iterations" from alternate realities show up in say Wild Magic zones as a way to mechanically challenge the whole party from time to time (ok, everyone, you're still "you" is a sort of essential level but this you is an entirely different class and background, consider it the elseworlds you) ... maybe after some time is a zone, a player who proved themself adept at this, with the players consent could be permanently hosting the wild magic that brings out iterations of itself.

So my Dm asked me to play one.  I am not multiple personalities I am many souls trapped in the same body.

Tips: Have a prop for each personality
Examples: When I am Wrecker the barbarian I put on a leather bracer at the table, When I am Fetch the bubbly theif I wear a red scarf.

You need a distinct voice for each character so the group isn't confused.

You are there to enhance the experience not steal all the best moments for yourself.  If you find yourself in the spotlight too much you need to pull back and let others shine.

Clear triggers controlled by the PC's at the table and the DM NOT YOU:
A Trigger for Fetch the rogue is when someone says: Treasure:  She bursts out and always says the same thing, "Treasure I love treasure!"  Fetch has a feat that lets her identify so the PC's use her whenever they get loot.  It started as a mystery but now that they understand one of her triggers they control when she comes out not me.

Consequences and retreat triggers: Wrecker is a barbarian who comes out when a child is in danger or when the priest of the group goes down in combat.  The issue was our priest was always going down early so it was Always Wrecker in combat.  Until they crossed a planar boundary bordering the Abyss.  Wrecker has a back story he doesn't like to talk about he spent untold years fighting in the blood wars and wont ever go back.  So when the priest went down Wrecker said in his clear weak voice I'm sorry priest I cant ever go back.  This moment lands hard>

Now its a fun roleplaying for the table:  They are trying to discover my character's triggers so they are in control.  What makes one come out and what makes them retreat they are in control so they never feel like I am just getting to play every character.

FLAWS: Do not make optimized characters make horribly flawed broken individuals.  Wrecker has an INT of 7 He is an idiot and acts accordingly.  Fetch is so innocent she tends to believe anything people tell her.  You know that class that everyone hates because it kind of sucks those are the ones to play with.  Again you are not there to steal the spot light!

Your DM has to trust you and be very informed and cool about it.
Share HP, Share Spell Slots:  This isn't a get out of jail free I am 100 characters free card.

The "Main" is a sorcerer:  If I turn into Wrecker and take 45 damage that is a problem because the sorcerer only has 30 hp and yes they carry back.
If Fetch casts a spell I lose that spell slot on all the characters.  It needs to be balanced it needs to be fun for everyone.

DO NOT make any personality a class someone else is playing:
My group is a Cleric, Druid, and Ranger.  So hard fast rule no personality can be a healer, a shapeshifter, or beast focused character.
My DM and I came up with a reason why but you cant come in and steal other peoples thunder thats not cool!

Bottom line if its not enhancing the experience for everyone its not a good idea.

I will add to the masses saying not to make a character like this.

Firstly, there's the insensitivity around making a real world disorder into a gameplay quirk for your character. This can be alleviated with fantasy reasons, like demonic possession, multiple souls (maybe you were guided by the souls of your ancestors, then your soul was stolen and they stepped in to get it back), or being a single-headed reincarnation of an Ettin.

Secondly, there's the time and spotlight and power you will be gaining at the table by changing classes and abilities all over the place. It's one thing to have multiple personalities in the same frame, but you're on about different abilities for each persona, which means you might blow all resources as a spellcaster to suddenly flip to being a martial. It'll make you more powerful than everyone else, and that's bad.

If I were to try and make a character like this, I would open with the above - they are not sufferign a real-world disease, they are fighting a demonic possession or something, and I would pick a class with features you can use in multiple ways. A Swashbuckler rogue, for example, can either lurk and strike like most rogues, or they can charge in with bravado. Both are viable, and it means you're changing the roleplay side rather than your hitpoints, mechanics, resources, etc.

Overall, I say don't do it, and certainly not to the extent you're suggesting. 

As DM i would never ask a player to play such character and if one was to ask me one, i would probably refuse as it's very sensitive and prone to cross people soft/hard limit.