What Causes Trembling In Hands Along With Loss Of Memory?

My boyfriends hands tremble often, and he says when he draws sometimes he cannot control it. I also noticed he is extremely forgetful, many times when I speak to him I end up repeating myself slowly so he can understand me. He also sometimes suffers of sudden headaches whether he is awake or asleep, usually on one side of the head. He feels like his legs will collapse if he doesn t walk quickly. He also has problems with maintaining an erection and does not respond to medication for it.