"It remains something people find out about only after these men are dead," says Dr. Park Dietz, a forensic psychiatrist who's been studying and writing about the phenomenon for more than 30 years. And while it's impossible to know how many deaths from AeA are mislabeled, Dietz says, it's common for the authorities to record them as suicides rather than reveal the more risqué truth.

An act that combines choking and sex may sound like something exported straight from an S&M dungeon, but it's not. The payoff is not so much psychological as physiological. The neck is home to two vascular superhighways: the carotid artery, which carries blood to the brain, and the jugular vein, which carries it back to the heart. If you constrict these vessels, carbon dioxide builds up in your brain, creating a narcotic effect. Combining that with an orgasm may trigger a dopamine release that intensifies that euphoria—"like taking Ecstasy and having sex," says Dr. John Sims, director of the neurocritical care unit at Massachusetts General Hospital. Occasionally, you pass out—and if that happens while your neck is still constricted, you will die. If, however, you survive, you will likely be overwhelmed by the magnitude of the feeling. In other words, this isn't some masochistic desire to be choked. This is a far more universal longing—to feel good, despite the risks, which include not only death but also damage to the brain caused by oxygen starvation.

Two years ago, newspapers and morning shows were abuzz with talk of the "choking game"—a school-yard pastime in which kids, seeking a euphoric high, would strangle one another until they passed out. Scott Metheny, a Pennsylvania police officer, responded to the phenomenon by helping to start an anti-choking-game website called GASP and teaching police officers and coroners how to recognize cases of death by AeA.

"Basically, the choking game is the gateway drug to autoerotic," Metheny says. "People are experimenting with asphyxiation play—without the sexual element—because they're told it feels good and they feel no damage from it. They put the two together because someone tells them that the orgasm will be so extreme that a regular one's not good enough anymore."

For Jeremy Ellman (not his real name), a 47-year-old real-estate agent in Long Beach, California, it all started with a parachute. He was 13 when his dad brought one home from an army-surplus store.

"I just rolled up really tight in this thing and it accidentally slipped over my face," Ellman says. "And it was very exciting." Pretty soon, Ellman was wrapping pantyhose around his head—sometimes more than five pairs at a time—to constrict his breathing, crawling into sleeping bags backward, and getting himself off "just by wiggling around." Back then, he didn't understand why his orgasms were better. But by the time he was in his twenties, he did—and he was chasing them every day. "When I had girlfriends, we did crazy noose play. I'd have them string me up from the ceiling, and then you kick something over and dangle there trying to catch your breath." Today, Ellman says, he's just your average California dad with a secret. "If you met me, you would have no idea," he says. "I wear Tommy Bahamas, flip-flops. No tattoos, two kids—absolutely normal."