Plus you don't actually go to sleep. Your eyes stay open. You are just really really relaxed.
Edit: Let's clarify: When people go into hypnosis they do not just "fall asleep" or slump over. That's not hypnosis. Their eyes stay open and whatnot. It's just that now they are a lot less aware of what is going on around them and whatever you say, they tend to believe. You don't just say "All right, now do the Irish Jig." No, you have to say "You're in Ireland in a pub, and everyone gets up and starts dancing..." etc. etc. If the subject doesn't like dancing, you can't force him, unless you do something like "A beautiful woman appears next to you and says, 'Would you like to dance?'" to get them to want to. Basically you spoof their senses and make them think it's all real. However, they will not really interact as much with their environment. Tell them that they're on a beach and they're in a swimsuit, and you'd think they'd jump in the water, but really, they won't. That's not how it works.