Checklist of specific actions you can do to maybe help with those possible reasons:
go eat something, if no energy/executive ability/else eat ingredients. no need to make a full meal, any food is good
new hyperfixation and no time for it
rotate concepts/blorbos in head. prime yourself for excitement once you're able to engage with hyperfixation
have not done a creative in 24 hrs
go do a creative. any kind, no matter how small or unrefined, is gonna feel wonderful
headphones, find somewhere quiet or replace with good sounds (I play brown noise in supermarkets to not get overwhelmed)
clothes are touching my body
if at home - change into sensorily safe clothes, if outside with no means of change - try to find a different sensory element to focus on. I stim with my neckless to distract my brain with a fun sound and well known texture. alternatively: find a not busy toilet stall and just take off an article of clothing for a few minutes.
safety blanket, hoodies, tea with spices, hot shower, hot water bottle/compress
find a quiet place. if an excuse is necessary, say you have a very important phone call (i generally say a medical appointment), it should buy you 10 mins of relative peace.
one (1) comment is stuck in my brain like a popcorn kernel
people often lash out due to insecurity, misplaced emotions, and no coping skills. they can also be callous and unfair without realising it. none of those reasons involve you, therefore, shouldn't matter much. try and pick that kernel out with positive feedback and constructive criticism that can help you grow.
last time I drank water was ??????
go drink water, but if you can't, any beverage other than alcohol and seawater will do. all drinks have water in them and will help hydrate you.
nervous nervous nervous nervous
tense your whole body as much as you can for a bit and then relax. this tip very much works, i use it whenever i find myself chased by the very slow tigers.
got a Slightly Worse grade than expected
is this grade gonna have a permanent impact on your life? 99/100 no. Sometimes we mess up and that's alright. your worth as a person isn't based on your gpa.
go hug someone. if there's no one available to hug, hug yourself. pet your own head, draw patterns on your arms, put your hands on the opposite sides of your face. the feeling is close enough to help you in the moment.
sleep. its the most important of step of actually feeling better. if you can't sleep, even laying with eyes closed with reduced stimulation is very beneficial to your brain.
talk to people. best in real life but if that's not doable in the moment, text people. if thats also not an option, i genuinely suggest getting on voice chats on discord.
guts are shredding (again)
meds as advised by a medical practitioner, make sure you drank enough water and that you ate enough food. Chicken soup is easy to make and a polish grandma's classic for an upset stomach.
have not seen sunlight in 24 hrs
go outside for a short walk. try and find a cool leaf/rock/trinket. sit on an outside bench and play a game on your phone. if too little energy for that, sit in the sunniest place in your home, or sit just outside your home.
sadly I can't help much with that. focus on the thought that you'll be out at some point.
try to read a book, try some arts and crafts, put on music and look for a non-virtual activity. write down a recipe on paper and cook something for later.
stim stim stim stim. channel the energy to settle it down
start with the bed. have it be your safe break spot. then deal with dirty dishes. then take out any waste. then put the laundry in a place you designated for it. just by giving yourself a safe sleeping environment and getting rid of any bio hazards, you improved your situation by a mile. take as many breaks as you feel like, while in the moment the task may seem completely overwhelming, you are completely capable of doing this. break down your tasks to the smallest steps and you'll be fine.
have not talked to Person in a while
talk to Person. they probably want to talk to you too
go on a wikipedia deep dive. watch a documentary about a subject you're unfamiliar with. when was the last time you tried writing a limerick? all brains require adequate stimulation, especially adhd brains. approach a new subject with trained curiosity.
imposter phenomenon (again)
while it may feel like sometimes we're not skilled enough to be in a certain space, other people are not that dumb. if you weren't supposed to be there, you wouldn't be. if you're the least skilled in a field, then you're surrounded by people from whom you can learn. if thoughts are too stubborn for that strategy, switch it over into glee that you managed to trick everyone even though youre unqualified. check you out, you mastermind of social engineering! if that also doesn't work, think about how often people get into a position that they very much aren't qualified for. one more person isn't going to collapse society.
create a micro routine! go somewhere at regular times. designate a time for meeting people/hobbies/activities. go through motions as if you had a typical routine.
how long have I been working???
stand up, go get some water and a snack, stretch: back, neck, wrists. look at something far away for a minute to reduce eye strain. if after bedtime - work can wait. i know it can be tempting to keep working while the motivation is there but by exhausting yourself you're gonna make your executive dysfunction worse. most of the time its a marathon, not a sprint.
take time to decompress. change plans if necessary. Too Much Socialization is an issue even neurotypicals experience. its perfectly normal.
Every step towards feeling better is a good step. Even small ones will make you feel better than before!