As everybody else has said, Sleep Paralysis is there to stop you from doing things like this. I certainly wouldn't want to get married to a woman, sleep with her and just about to doze off when she punches me in the face screaming "TAKE THAT CUPCAKE MANANAN...gghh...". In fact, that would be rather intresting...

Anyway, I guess you could hurt somebody if you suffered from sleepwalking and the like, but I expect it's a pretty rare occurence. Murdering people in your sleep - probably dosen't happen. For example, a husband and wife don't often dream about murdering each other (because they love each other, duh), so if they suffered from sleepwalking, they probably wouldn't act out anything like that. Even if they did they would probably stop.

And it's not every day you sleep near to somebody you dream about murdering. So, yeah.