I don't agree with Beastmaster. Besides the fact that I could hardly understand what he said because he has no grammatical sense, blackjacking and backstabbing mobs would be a very hard thing to abuse. It would be very time consuming, and a person could just level differently and get faster experience.
The principal of the fact is, if you're asleep, you are not too hurt and weary to be backstabbed. You are a sitting duck. You are bait waiting to be stabbed in between the vertebrae.