Originally posted by Hikaru
But what I mean is like, if a door behind you just slams and you dindt expect it, would you, like in the real world, jump up becouse the sound scared you?
No, this shouldn't be possible. Your body is literally paralyzed while you sleep, presumably to keep you from acting out your dreams. This would prevent you from "jumping" in your sleep, although you still maintain control over your breathing and eye movement while you sleep, so an observer might notice a sudden change in your breathing or see your eye lids twitch, possibly.