After a transplant, you are usually on immunosuppressants for life. Some of these can be quite poisonous, and could be affecting the brain. Certainly prednisone (nearly always part of the mix) can do strange things to thought processes. My wife has had "steroid psychosis" on prednisone, and some of her behaviour is only funny in retrospect. She did finally work out how to redesign the kitchen, though.
"Better living through chemistry"?