Autistic burnout is serious and can lead to permanent loss of skills. It's in no way your imagination, nor are you alone. I was permanently disabled by burnout in my 40s. I also knew someone (now sadly dead) who became permanently non-verbal in their 30s due to burnout. Don't let anyone convince you that it's not real.
For me, I suspect some of my skills are gone for good. For example , I can't speak on the telephone at all anymore and I'm pretty sure I'm not getting that back, though I used to work in Communications and spent half my life on the phone. I've gotten some of my life back by living a slow-paced, autistic friendly life. For me this meant moving to a very rural area, but I know this won't be an option for many in burnout.
On another note- in the future, if you want to cross post between Lemmy and Reddit, would you mind copy-pasting rather than forcing people to give Reddit our page views in order to see what you said? Many people on Lemmy no longer want to give Reddit any traffic at all- that's why we're here and not there.