Open Question: My boyfriend sleepwalks and is at times violent...?

My boyfriend and I live together and there have been several incidences where my boyfriend has been sleepwalking and has covered my face with a pillow saying "I'll fucking kill you!" and has punched me in his sleep while yelling "I'll beat the shit out of you!"... It's happened a total of five times now, I know this because it's scared the crap out of me each time. I know that when he was younger he destroyed a fan while sleeping so I'm really worried that he may try to hurt me further. What bothers me the most is that when I'm all shaken and he's out of his sleepwalking phase, he doesn't seem to believe he's done what he's done. He's not an alcoholic, however does frequently smoke - if that has anything to do with it? I don't know what to do to stop this from happening. I'm becoming afraid for my safety. Please help.