Just a hunch, but he may be experiencing ATONIC seizures or sometimes they are called "drop spells". You say he gets right up afterwards and is ok. These drop attacks are caused when the brain doesn't send the proper signals to the body and he loses muscle control for a brief time, a second or two, just enough to cause you to fall. It's hard, but try and get a look at his face, if you can, when he's going down. I saw my brother in law's face once, he has these drop attacks, right as he was getting ready to fall and I knew that look from dealing w/so many people w/other types of seizures, including how people told me I looked when I took a seizure. When I mentioned it to my sister, it dawned on her that "yea, you had that same look when you started taking a seizure". Try if you can and if you do see his face, and if it looks strange, can't describe it, tell the GP and go from there. I hope this info helps. I'm not saying he's having atonic seizures, but it's a possible answer. That's what my brother in law is being checked for now. He's been checked for everything else and nothing. Hope everything turns out for the best and you get the correct diagnosis. If he continues to fall and keeps hitting his head, things could get alot worse. Best of luck to you and him.