Yeah the theory that general anaesthesia doesn't put you to sleep and numb the pain, it only paralyzes you and prevents you from forming any memories. So you remain awake and feel all the pain of surgery, you just can't scream and you won't remember it.
The only reason I doubt that theory is because the pain would cause the heart to race which would be noticeable on the monitors and other autonomic effects like sweating and vomiting.