Why are you chosing to write about something about which you have absolutely no knowledge?
What appeals to you about this topic?
Truthfully, I think it's impossible to answer your questions. Too many variables are involved--including the fact that your character has serious psychological problems.
If you are really interested in the subject, perhaps you should visit a rehabilitation center and observe first-hand the effects of severe head injury and brain trauma. Beforehand, do a great deal of reading and familiarize yourself with basic neuroanatomy and neurophysiology so you can ask the staff reasonably intelligent questions, regarding brain functions, to get the answers you are seeking. Then you can decide whether you are up to tackling this topic.