What they don't tell you is you are basically dead. They are keeping you alive while under. You are NOT sleeping. When you sleep you never lose the sense of "I" or "me". When you go under general you do lose it. This is why surgery takes so much of your energy.
The gen. anesthetic for my cancer surgery seriously messed up my cognition, including memory. It gradually improved but I don’t have it all back. For weeks after the surgery I was a stumbling retard. I did research and found some people lose it all permanently, some aren’t affected at all, and everything in between.