I used to ask my players what they like about D&D so I could be sure to include those things in the adventure to "ensure" it was a "good session". If they like a lot of interaction with NPCs I make sure I've got a bunch of fun NPCs ready to throw at them. Maybe they put a lot of time in their backstory so I make sure that comes up in the sessions. But there's been a lot of times where I try to cater to the player's preferences but I notice player's zoning out or not really having fun. I realise I should pay more focus to things that drain energy for some players.

Some draining elements could happen before the game even begins. Some might find it draining when other player's show up late. Or maybe if 2 players are coworkers and they can't stop talking about work. Or maybe they find it frustrating when someone forgets to bring their dice or charactersheet.

I personally find it draining when people interrupt eachother all the time. If it's in character it might be fine, but if it's just to make fun oneliners out--of-game it can suck all the tension or emotion out of a game. Or when people are talking about something completely different when someone else is trying hard to figure out a puzzle in the game.

Maybe it's certain topics like animal cruelty. I know for a fact that some of my players wouldn't appreciate me killing a wolf in the adventure and it would set the mood for the rest of the session.

TLDR

What are things that would drain your energy when playing D&D? What type of situation would result in you zoning out and not interacting with the group or the story. What would cause you to not have fun?

When one phase of the game drags on too long I feel my interest wane.  For instance if the role play is going on and on with meaningless banter that does not relate to the plot I’ll start to check out.  Or if combat isn’t moving very fast and folks are taking too much time deciding what to do.  Or it could be exploration, like if we run into a puzzle that no one can figure out and is taking forever.  

As a DM I’ll keep a sense for this and move the game to a new phase of there is a drag as smoothly as I can. 

Slow combat is one that can do it for me. If someone is taking forever to decide what they want to do. Or if there are a ton of npcs involved etc. 

One thing that almost killed a session for me was just a matter of bad dice luck. A mind flayer mind blast stunned my character through the entirety of a 45 minute encounter. All I could do was once every 8-10 minutes was roll a saving throw and fail, and by the time I got out of it, the encounter was over. That was very frustrating, though not something that applies to normal sessions. 

• People unable to focus on the game
• People unable to remember what happened 10 minutes ago
• Players that don't know how to play the game in spite of having been playing for years
• Not enough combat/danger - Heavy roleplay. I feel a session is "wasted" if there's no combat.

When the Warlock, who has no spell slots, spends 10 minutes switching their gaze between the board and their character sheet, deciding what they're going to do on their turn in combat, before eventually picking Eldritch Blast. 

RP stage hogs drain me.

When combat takes too long 

People who can’t do simple math quickly. It should not take long at all to add +7 to your d20 roll FFS. As a corollary to this one: people who can’t do simple math quickly but won’t listen to the people who can. The answer is 23, like I just told you four times in the last two minutes since you rolled but you insisted on taking forever to do it yourself because reasons? Grrr. OTOH, I could totally see where some people might be drained by impatient others “rushing” the die roll results out of them…lol

Having engaging NPCs helps me. Feeling that there is depth and that I'm in a world that I can explore. So the opposite if those I guess. An uninteresting world with cardboard cutout NPCs.

When people take ages to decide what to do. The more players there are, the lower my tolerance is. Nothing peeves me more for someone who takes an age to make an obvious decision.

Things that drag me out of the game and break immersion. I prefer to level up at the end of a session if possible for that reason.

Being locked out of an event. It would just frustrate me if the thing happened to Nyr happened to me. On a related note, constantly missing. Actually, that depends, it could make it funny, but it can be something that would upset me.

Rules lawyering in a fight or interaction. I don't mind discussing the rules and even enjoy it, especially if I learn something new, but please, let's just focus on what's happening in the game.

Just a few things!

Players who don’t know their characters and then basically the rest of the table needs to tell them what they can do. 
Though I do make allowances for new players. There’s a point where you shouldn’t have to say, I cast X. And then look up how it works, and then say, I actually cast Y, and then look up how it works before finally saying, I just cast fire bolt. 

Players who are overly critical of other players. It is most commonly observed among the more experienced players, sadly.

Being shut down. Sometimes my character drops to 0 HP. The rest of combat is me doing death saves. Sometimes the DM doesn't like us winning easily, so he just directly shuts down some character abilities. Sometimes the DM wants the story to go a certain way, but instead of stating it plainly, he shuts down every other action.

Needless lore dumps, especially when it's not even in character. I'm talking about when people wanna go on for five minutes about the hierarchy of devils, when all we're trying to do is remember whether a barbed devil has cold resistance.

Being overly beholden to the battle grid. Like we can tell the cone will get 4 guys in it, but we still have to put it on the map to make sure. We can say we're going into a room, but there's this awkward silence of confusion if we don't all move our tokens. Nothing is real if it isn't shown on the grid, and nothing can be attempted that doesn't make sense on the grid. We're not asking "what do I see," but rather "what's this square thing on the map?"

Unending references to other media.

People not giving others a chance is draining on me. I've seen a fairly new player lose all her confidence because she used a fire attack on a fire-based enemy, it didn't work, and another player basically said that it was obviously not going to work because they are a fire type enemy. Players need to allow newer players to make mistakes and learn from them themselves, not to make mistakes and then be bombarded with all the reasons everyone else already knows about why it was a mistake.

The biggest drain for me is people not paying attention. Hasn't come up recently (thankfully) but when a player has to ask the DM to repeat something that they just said because they were distracted by phones (grrr) or chatting, that bugs me, because I want to keep going and we already know this, even if you weren't listening!

I find it really draining when a character/s endlessly try to de-rail a plan of action put forward by one other member of the party, or trying to kill/attack an NPC that is actually trying to help the party.

Having a single player who thinks that their character is the protagonist and constantly hogs the spotlight, regardless of whether the situation in question is something they're competent at.

Having to actively pretend you don't know something to prevent metagaming. (e.g. even though you've been playing for years and know the abilities and resistances of the monster you're fighting, your 1st level character wouldn't know)

Quote from Grunk999 >>

Having to actively pretend you don't know something to prevent metagaming. (e.g. even though you've been playing for years and know the abilities and resistances of the monster you're fighting, your 1st level character wouldn't know)

 And the inverse: getting accused of metagaming over things that someone would reasonably expect a person who lived in that universe to know, like that you need to use fire to kill trolls.

Having players not understand their character's abilities. It is hard enough to be a DM, I cannot keep track of players not knowing their own spells properly either!

Quote from 6thLyranGuard >>

Quote from Grunk999 >>

Having to actively pretend you don't know something to prevent metagaming. (e.g. even though you've been playing for years and know the abilities and resistances of the monster you're fighting, your 1st level character wouldn't know)

 And the inverse: getting accused of metagaming over things that someone would reasonably expect a person who lived in that universe to know, like that you need to use fire to kill trolls.

 but is it common knowledge really?   The internet is rife with examples of people displaying a distinct ignorance of things most would consider not just common knowledge but sense as well.   So... An INT check is not out of line for something like that.