I have time-lapses in my life where I don't remember anything during that time. I believe severe mania/psychosis does great damage to the brain. Sustained stability usually brings back better cognitive results.
When I forget what I wanted to say, I always tell people sorry "my brains fried."
I'm lucky that I still have the ability to read books, it just takes a lot longer then it should.

It is true that our brains have the ability to rewire themselves. Unfortunately, meds have cognitive side effects. However more damage is done from our episodes.