It sounds like something out of a lurid crime or science fiction novel, but it is a real, albeit only recently recognized, sleeping disorder. It's called“sexsomnia,” and the people who suffer from it engage in sex while asleep.

The clinical name is NREM arousal parasomnia. The acronym stands for “Non-Rapid Eye Movement,” and parasomnias are the class of sleep disorders that includes what we popularly describe as sleepwalking and sleep talking. Sexsomnia is a recent addition to the family, written up for the first time in a 1996 paper by three University of Toronto researchers.

It is still not known why people suffer from sexsomnia, but scientists do know that it shares the same triggers as many other paranomias. These include recreational drug use, stress, alcohol consumption, and sleep deprivation. The more of these in which you engage, the more at risk you are.

Still, sexsomnia is not very common. Only 6 percent of all adults are inclined to have parasomnic activity, and sexsomnia sufferers are a sub-set of the sleepwalkers. Interestingly, an estimated 15 percent of the child population engage in some parasomnic activity, yet psychologists view this as normal in that age group.

In the legal world, sexsomnia is being treated like sleepwalking as well. It has become an accepted defense against some alleged rape cases. In one such case, the court ruled the sexsomnic act as “non-insane automatism,” and acquitted the defendant because he had no conscious awareness of his actions.

The study of sexsomnia and related paranomias is teaching psychologists plenty about the nature of the unconscious and semi-conscious world. Traditionally, scientists viewed sleep as being divided into four primarily discrete phases: a dreaming REM state, the deep-sleep NREM phase to which sexsomnia as been assigned, the transition from wakefulness to sleep called hypnagogia, and the passage from sleep back to wakefulness (hypnopompia). Parasomnic activity during NREM sleep skewers these tidy ideas and some scientists believe the sleep/consciousness model may need to be replaced with a range of intermediate states.

If you are diagnosed with or feel you might be prone toward sexsomnia, avoid the stress, alcohol, drug and sleep deprivation triggers that can trigger episodes of the condition. You should also address any underlying sleep apnea: lose weight, quit smoking, and get hold of a continuous positive airway pressure machine. Taking medication to induce sleep may also be problematic. Researchers have concluded that some kinds of sleep medication can trigger parasomnias. In any case, you should check with your doctor before starting or stopping sleep-inducing medication, even over-the-counter ones.