It's impossible, I simply don't have enough cognative power to invent some of them things I know. You're implying I managed to invent within my mind several languages, numerous numerical systems, ancient history spanning thousands of years (admittedly, obviously I don't know all of it, but the point remains), the laws and operation of science within our universe from theoretical physics to evolution, and more inbetween. If this scenario ocurred, I would likely either resume insanity due to the overwhelming nature of reality, since it would conflict with how I percieved fundamental truths for years, or I'd... see if what I invented makes sense in context of this world I'm "reborn" into, and then spread what my apparantly incredible mind managed to concoct from nothing.
If I turned out to be considered an invalid and what I understood was less than that of the average child of the race I was a part of, then I'd be sad.
Probably resume insanity though, I've made so many friends, done so many things, and worked towards so much, if this was an hallucination, dream or "lie", I don't think leaving would leave me useful. It's optimistic to imagine maybe that I'd wake up to a much more elaborate and awe inspiring world, but dayum would it be at the very least interesting.
If I awoke in Middle-Earth after being released from magical imprisonsment within my own mind, I might be pleased
