As nerve signals travel toward your mind, they're just raw information, out of context other than the biological "instrument" readings they represent. It's not until they get to the brain that the decision is made to interpret them as pain, pleasure, or something in-between. What most people feel as pain is simply "more sensation" - it feels good until it goes too far. With training and willpower (and yes, it's true that few people have quite that much willpower), these intense feelings can be felt as exhilarating ecstasy rather than horrific torture.

That's all fine and well when you're privately amplifying your sex life beyond what the average cock and balls enjoy, but it becomes a very different scene when you let those games loose in the middle of a drunken office party.