What mental disorder is this?

theres a phenomenon called "transitory amnesia" (I think) where you do just lose a few hours and get confused. A friend of the family had it and his family were dead scared. He was about the same age as your dad and he got all confused on the way home from work, and then couldn't remember what had happened afterwards. Its not well understood and in most people that get it, it never happens to them again. I'm not sure if this is what happened to your dad or not. Was your mum there at the time? She might be able to remember what the doctors said.