i have several that look like that, going to sound goofy but the plant has a 50/50 chance of surviving and if it some what recovers it may not fruit . quit watering it and make sure it gets some direct sunlight. you want the soil dry. the cold damp soil is what will do the kitten in.
i always have the dilemma at this time of the year with plants like this: should i kill it off and start new or take a chance that it will regrow?? most of the time killing it off is the right answer - even if it was your last seed of the variety, seed is pretty cheap and easy to get. i have a peach kitchen pepper that i let stick around hoping it will regrow and produce new fruit - failed me last year and still hanging in for this year..... as of now.
Something in the soil most likely, nematodes?
If you haven't tossed it yet you must be wanting to keep it around. Drop the whole thing in a bucket of water and rinse all the soil off the roots. Drop it in a 2nd bucket of water with some hydrogen peroxide dilution. Repot in a fresh container with fresh soil. Throw in a handful of DE if you can find it. Don't use granular fert, use high quality liquid at 1/2 strength of the lightest recomendation and see what happens.
Give as much sunlight as you can find this time of year, keep it warm and not too moist.
Don't fert - fresh potting soil has plenty of nutes. But indeed, rinse in luke warm water to get rid of all the soil. Check for larvae, eggs, bugs, mold etc.
Put it in the brightest light you can offer (realistic, don't toast it).
I repotted it in fresh soil a month ago and added lot more vermiculite. Too cold outside and its under the full spectrum lights, not much sun lately. I do want to keep it it has nice gnarly base. I did add a little nutrients so its richer. Temps are going up so see if that makes a change, trees are budding out side even though at night it goes bellow 0c.
Thanks!