Is anybody else reminded of the character from the song "One"[1] by Metallica, and the movie/novel "Johnny Got His Gun"[2]? Granted, that was different in that the situation resulted from a traumatic injury and the man lost his limbs. But the idea of being "trapped in your body" - unable to communicate, aware of your own existence, but basically nothing else - seems similar.
Darkness imprisoning me
All that I see
Absolute horror
I cannot live
I cannot die
Trapped in myself
Body my holding cell
I remember being terrified of this idea the first time I saw the video all those years ago. I guess I still am. I just had no idea - until now - that a situation like this could result from much of anything other than a major traumatic injury.
[1]: https://www.youtube.com/watch?v=WM8bTdBs-cw
[2]: https://en.wikipedia.org/wiki/Johnny_Got_His_Gun_(film)