My ex used to do this all the time, but only when she was falling asleep...not when she actually went to sleep. We'd be layin there, and all of a sudden she'd kick the shit out of me, and be like...did i just kick you? Sorry. Then when she fell asleep I'd stick things in her butt...that was a lie actually, but she DID have the twitching thing.
She's asked some doctors about it, no one knows though.