Hypnosis has been around for centuries, and has long been misinterpreted into something else by Hollywood. Hypnosis is a do with rather than a do to process. You cannot hypnotise someone, like a surgeon can cut someone open. What you can do is provide the assistance for someone to go into hypnosis.
Hypnosis is simply the act of changing into another state of consciousness. Merely the act of closing your eyes changes your state of consciousness. This is how you see the difference between reality (eyes open) and dreams (eyes closed) there is more to it than that, as the brain activity changes from beta to alpha waves.
There is a matter of something called the critical faculty or critical factor, which is the safety mechanism to prevent bad things happening to the individual while they are awake and in reality mode. In dream mode, this safety mechanism is not needed. In psychotic patients and those who have artificially altered their mind state with drugs have this mechanism turned off.
Hypnosis works by bypassing this critical faculty.
Somnambulism is the state that shows that the critical faculty is bypassed while the patient has their eyes open. There are several bizarre things you can do in Somnambulism. The patient can be fooled into believing they are awake, in much the same as sleep walkers think they are awake when they sleep walk.
Beyond Somnambulism, the conscious mind goes to sleep. In Esdaile, the brain changes its activity to theta and the patient experiences a euphoric reaction. The subconscious is awake of course, and helps to make change to the unconscious. Beyond Esdaile into Sichort is another sleep state for the conscious mind, this time the brain changes its activity level to delta.
Since the subconscious is still in control, the body functions perfectly. In fact, since the conscious mind is the part that causes problems for the body, it performs much better than when conscious.