Anesthesia, being knocked out, unconsciousness...what does the Buddha have to say about it?
The mind is always reacting to sensation on the body what every any state you are in, including but not limited to anesthetized, knocked out, unconsciousness, etc. Only time you do not sense any sensation is when you are in Pala Samapathi. So you are always have some level of awareness of the body through sensations at the deepest level of the mind or subconscious mind. At the surface level (conscious mind) you might not be aware of it.

Also see: From the Deepest Coma, New Brain Activity Found