Have you ever been hynotized? I was, once. It wasn't what I expected. It wasn't like being asleep or absent from my body or made into an automaton. It wasn't like the hypnotist said "take off your shirt" and my hands moved without me, or I felt compelled to do it.
It was like I was totally awake and in control of myself, and I freely decided that taking off my shirt was a thing I wanted to do.
Sometimes I have that same feeling during sex. I'm a totally rational and free mind, and if I so chose I could be totally stil and silent and unmoved. I just decide to thrash and clench and moan and scream, is all. To some small exent this is true--when my roommate is home I rediscover my volume control, and although I'm not exactly silent I do manage to hold in the more unholy howls. Although other times I want to be quiet and the best I can do is clasp a hand over my own screaming mouth. Like it's someone else's.
The strangest is when I have those hyper-orgasms, the ones that knock me flat so I can't move or speak right for a few minutes afterwards. During that time, when I'm crashed out quivering and babbling, I'm completely aware of myself and a little chagrined how ridiculous I'm acting. I could just decide to pull myself together at any moment... I never fully understand why I don't.
Altered states are like that, though. They always seem real and ordinary when you're in them; a person with schizophrenia or tripping on hallucinogens, or even just dreaming, doesn't experience just images but the knowledge that those images exist and make sense.
(Or maybe all of existence is like that. Right now, I have the sensation that everything I'm experiencing is real and sensible and I'm in control of myself--and that proves what, exactly?)
Maybe the line between "the devil is talking to me through the rats" and "oh god fuck me fuck me fuck me" is a whole lot finer than I'd like to believe.