https://en.wikipedia.org/wiki/Ghost_in_the_machine
^-- I'd be hard pressed to think of a situation which more greatly highlights the difference between those two. I don't mean that the mind might not want to cum (that can certainly happen, but it's just as likely that the mind wants to cum too).
I mean that you can sense your body fighting to wrest control away from you (as a sentient being) and function on instinct as its own independent entity and if you give into it, you feel yourself taken along for the wild ride.
The best analogy I can come up with is a fictional scenario and a totally different mood, but when the unit in Neon Genesis Evangelion go berserk. The pilot's still in there, but the pilot's not the one driving anymore.
It's an amazing sensation and one I only get, like some others have said above, when cumming inside a woman and we're not using condoms (her being pregnant doesn't stop the sensation from occurring, but wearing a condom does).
I think there's a tendency of guys to exaggerate in a lot of these kinds of threads, but on this particular topic even the more outlandish replies so far don't feel like they're stretching the truth. It's just an amazing experience and there really is nothing like it.