Oh, I totally, completely understand this stuff.
FIREd in 2015, after working around 20-ish years, extremely high level of toxicity to the point where my supervisor (but not my actual boss until the last year) used to have fun playing the "maybe I'll get you fired" game at least once a year, and was big into the stupid, high school mean girl clique mentality. It was a horrible, terrible place and wasn't helped by being a major pressure cooker of constant project deadlines with required (unpaid or compensated) overtime; 70 hours a week was the average, and you were expected to cancel appointments, vacations, etc., especially if the golden ones decided that they couldn't complete their own projects at the last minute. I had to take work with me when I had to go out of state after my dad had a major heart attack. I was working in his hospital room and ended up getting an average of 2 hours sleep because I was told that the work had to be done or pretty much don't bother coming back...
I went into panic mode for around 6 months to a year after I finally quit. Not having never-ending lists of things to do, the structure, all the pressure suddenly gone - it felt wrong and the anxiety came on full force because I constanly felt like I forgot something and needed to catch up on it before some horrible thing happened. I developed severe depression and PTSD. I think by year two, things started easing back to feeling "normal" but I did have to do counseling and for a time there, over structure my daily schedule (errands, volunteer work, house work, etc) so I felt more in control of my environment.
I'm well into year three at this point and it's still just "okay" not perfect. I'm working hard at some things (exercise/health) in hopes that this will also help down the road. I gained over 100 pounds and had poor exercise habits, so concentrating on getting healthy became my mission the last two years. I may not be able to untangle the mess in my head very well so far, but getting my body figured out has helped. Added bonus is that no one I used to work with would even recognize me now (I've lost 140 pounds and look like a completely different person).
To this day tho, I can't even go visit the place. I get panic feelings just going in the area, so I've avoided it. And I still have nightmares. I am afraid I may always have them, but at least they're starting to fade and I have made progress.
But yeah, if you had a bad work environment, don't expect FIRE/retirement to be an instant cure. It may take years, not months, to get things worked out of your system. Don't be afraid to seek professional help with the untangling process either, because this kind of trauma/drama sometimes has far spreading, deep roots.