I need help with a friends sleep problem

I need some advise on this sleep problem that my sisters boyfriend has been having lately. It has happened about 5 times now. He will start groping my sister but be totally asleep. She has even woken up with him on top of her and he is doing things to her (without getting to graphic)and he is totally asleep. He doesnt remember a thing about it in the morning. It is bothering my sister and her boyfriend is even more upset about it. He feels like he has practically raped her. So what is the deal with this? Can anyone help? Also can you email me as I probably wont be checking these boards often.
Thanks