lol, you dont blame it ... your unaware and just as shocked and surprised as they are. the reason it happens is that the body is not immobilised which it usually is during sleep, however, because it isnt, your body is able to act on its dreams and and thoughts even if they are at a subconcious level.

you wont wake up if you believe its all part of a dream.

"If you are lying there dreaming about having sex with your wife and you just happen to be having sex with your wife then there's nothing there to stop the dream. You don't perceive that as wrong."
However, if something UNUSUAL happens, say for example, and alarm clock buzzing at 7:30am to get you up for that dirty for letter word (w-o-r-k), then you would wake up.