JuneBillie - so sorry you have to go through that with your dad! I've been there, done that.
I remember carrying on one sided conversations with dad when I went to visit, as he just sat and stared! (He had Parkinson's). I would look at that shriveled up man in that wheelchair and think - that is not my dad! He was a very muscular, solidly built man in his earlier days. Often I would end up in tears when I got to the car to go home.