What's wrong with me: I am playing so badly

Maybe you should try checkers...

Jaque, if this is still going on, don't be disheartened by 20 games. If it were over 1,000 games, then be more concerned.

Seems you're back over 1900 now.

legend: You're in good company... I haven't improved perceptibly in 10 years either. We're not going to go on improving forever.

You stop improving when stop learning. Legend said his skill doesnt improve even if he does tactics or read books. He is probably wrong.. At legend's or claymore's elo, a little but permanent improving in rank means enormous quantity of chess knowledge or tactic ability.
Is not like player at my rank. who can hover in the 1500-1600-1700 elo range because of a simply mood change a "bad day" wich i refuse to think too much, or by changing the opening-defense that i usually play...

Also, If you have not enough time to think, you dont gonna learn anything valuable from your games you 1 minute games are like fast food, taste good but isnt healthy.

tl;dr: you improve when you learn, even if your rank doesnt reflect it (yet)

There's an inexhaustible list of variables which affect your game. There will be ups and downs for the rest of your chess career.

Continu to read books (especially Jeremy Silman's), solve puzzles and maybe try some new openings.

Don't worry friend, No one is master of all openings and middle games even end games techniques, just focus on you game and try to understand what your opponent is doing and what he wants to do. try to understand the opponent's plan and strategy, and don't let him do that what he want to do.

spent some time on solving puzzles before playing, create your own repertories, if you playing white try to play scotch, Ruy, french or open position openings which will lead you to develop your army more quickly,

most important is first develop your pieces then plan to attack with backward and forward strategy, stuck you opponent with some tactical vision, squeeze him as you can...

You may visit my some recent games for reference because i was also in same condition a few month before, now i am happy

further to append this i appreciate Moggol1989 advice jeremy Silman's books are very impressing and having long term affects, you may also try to visit Mikhial tall games, these are full of tactics and surprising, i bet if you carefully view tall's games and try to implement his techniques in you own games, you will be +300 definitely in you current rating.

does anyone have advice on how to "snap out of it" when you have one of those days where you feel like you've had a brain amputation

i'm losing against 12XX players

i make the most stupid mistakes. it's like i'm having a stroke or something. i mean i'm not really great to begin with but god damn

The brain fog will pass.

Yeah, just don't play for a bit. Maybe do training. The more annoyed you get at how badly you're playing, the worse your play.