Patricia Payne, author of "Sex Tips from a Dominatrix," likens it to a runner's high. "Just like runners hitting the wall and losing track of their legs, people try to create that same sensation and reaction using pain."
For some that pain can even lead to an orgasm, she added.
Payne traveled the country for three years to research her book, going to designated clubs, S&M fetish association meetings and countless "dungeons" -- a place designated for S&M play. Most places forbid full sexual contact and every club has dungeon masters -- lifeguards of sorts in case of a mishap.
"People go to clubs or dungeons to meet like-minded people but also because of the equipment," she said. Blindfolds fit just fine in a night table but not wooden Catherine wheels, a vertical Wheel of Fortune-type contraption with radial spokes onto which you attach your partner.
Toys of all sizes are aplenty, including suede flogs, leopardskin handcuffs, paddles and whips (which take some mastering, according to experts).
Morgan Lewis -- also known as "Her Majesty the Queen" -- likes to play sex games with submissive men, but she stresses the importance of getting to know each other. "It's not any different from any other relationship, you share your likes and dislikes and you find out each person's expectations," she said.
Lewis, a curvaceous dominatrix, believes limits can be tested, but that it's her job not to take the game too far in her personal relationships. "Not all fantasies should be carried out," she said.
Most couples choose a "safe word," that signals to the "top" to stop a scene immediately. A word like "no" or "stop" may actually intensify a scene because it's part of the submissive fantasy, so instead a color code is often established.
The S&M community swears by its motto, SSC, which means safe, sane and consensual.
Critics of bondage, submission and the S&M culture believe participants are abusive, desensitized and sick. Not so, said Baumeister.
"There's no sign people who enjoy masochism are mentally ill at an elevated rate," he said.
Baumeister estimated that only 1 percent of the population engages regularly in S&M but that most everyone fantasizes about it. Overall, he said, more men follow through with their fantasies than women.
New York-based sex therapist and psychologist Dagmar O'Connor believes people who follow through with pain play are repeating early sexual imprints. "Either they were humiliated or they felt arousal or shame during a punishment and they want to relive the victim/perpetrator roles."
Dossie Easton disagreed.
"I don't think it's a pathological response because lots of people who like S&M didn't grow up with abuse or corporal punishment," she said. Easton thinks you can't even guess correctly who's a masochist or a sadist when people get together in street clothes because personalities rarely match the stereotypes.
For O'Connor, S&M in a controlled environment or in the privacy of your own bedroom is minor compared to the rampant self-abuse in our society.
"People put themselves at risk all the time doing drugs, flying airplanes, binging on alcohol and food, there's nothing wrong with having fun with sex."