Your mind is reliving traumatic events from the past, being haunted by confrontational yet unavoidable emotions.
---Before gaining this feat, establish with your DM what your character's triggers are, how they would affect their personality, and any details inbetween for the purposes of roleplay and resolution of future conflict within your character.
--- In addition, pick a few actions, spells, or traits that may come in response to a trigger should you enter into a mode of "Fight or Flight".
When a trigger visually or auditorially occurs within the limits you can see or hear, roll a wisdom saving throw. The DC for this save is 15 + 1x, x representing the number of times you have consecutively succeeded on a saving throw in relation to this feat. This is to emulate the bottling of emotions or taxation of emotions that can occur within yourself.
On a success, no severe effects occur. Your character will feel a bit off center for [roll]2d10[/roll] minutes, but will be able to successfully recollect themselves after the specified period of time passes.
On a failure, you enter into a state of "Fight or Flight".
Roll [roll]1d20[/roll]: On a roll of 1 - 10, you are put into a "Flight" state. On a roll of 11 - 20, you are put into a "Fight" state.
Flight - The trigger that occurred has put you into a state of unyielding fear for the next minute or until the source of your fear is eliminated.
If appropriate, one of the actions that was specified earlier occurs immediately and uncontrollably (targeting the source of your trigger if possible) as if you had a gut reaction to what occurred within split-seconds at the start of your next turn.
Then, you gain the "frightened" condition, with the source of your fear being who or what caused the trigger. If this trigger is to occur within 10 feet of you, you are "paralyzed" until the end of your next turn.
At the beginning of each of your turns, provided you aren't paralyzed, you must spend as much movement as you can to either break line of sight or move as far away as you can from your source of fear, and you dash if you can do so. You cannot willingly move closer to this source of fear. The emotions of this state can be suppressed by effects similar to that of the "Calm Emotions" spell.
After this state ends, your fear comes to a halt and you are slightly fatigued from the lack of adrenaline in your system. Your speed is halved until the end of your next turn.
Fight - The trigger that occurred gets your adrenaline pumping in such a way that you feel obligated to put what's hurting you to rest for the next minute or until the source of your fixation is eliminated.
If appropriate, one of the actions that was specified earlier occurs immediately and uncontrollably (targeting the source of your trigger if possible) as if you had a gut reaction to what occurred within split-seconds at the start of your next turn.
You have disadvantage against creatures/objects that are not the cause of the trigger due to your hyper fixation.
At the beginning of each of your turns, you attempt to harm the source of your trigger by any means necessary and with little care of your surroundings. The source of your fixation is unable to make you fear it or charm you for this duration.
You are unable to willingly move away from the source of your fixation.
After this state ends, your rage comes to a halt and you are slightly fatigued from the lack of adrenaline. Your speed is halved until the end of your next turn.
Once the duration of "Fight" or "Flight" ends, you cannot be triggered into either state by the initial source for the next 24 hours (this is to represent a potential numbing recovery period to that specific event).
Recovery - With the comfort of your party or your own self-care, you slowly begin to learn how to cope with your PTSD.
After a trigger occurs (or you are to discuss the emotions around your PTSD) and you take a long rest, the DC for your saving throw is permanently reduced by 1. The coping mechanisms that you are picking up are slowly becoming more effective after a bit of practice in your free bedtime activities.
You can also lower this DC by a specified amount that is deemed appropriate by your DM in response to an action that your DM also deems appropriate.
Once the DC gets down to 8, the value of x is no longer added to the DC amount. The chance of such events occurring after so many times is still present, but never zero. You are just nearly at terms with the events of your past.
Once the DC is at 2, you can remove this feat from your character sheet. The emotions of what have occurred will forever reside with you. Now, not as a burden; But as a book for you to recite at the end of your journey. Or when you die. Either or.