As sleeping disorders go, this may not be the worst one. Sexsomnia patients report having initiated sex while sleeping. Now scientists have provided a hint at the prevalence of this sleep sex.

Sexsomnia was reported by 7.6 percent of patients at a sleep disorders center, researchers reported Monday. Starting sex while asleep was more common in men (11 percent) than women (4 percent).

Previous studies have found that some people — mostly men — occasionally initiate sex with a partner and reach orgasm during sleep. They usually have no memory of such "sleep sex," as some researchers call it. They find out about it only if a partner tells them.

"There have been no previous studies of how frequently sexsomnia occurs," said co-investigator Sharon A. Chung in the department of psychiatry at the University Health Network in Toronto, Canada. "While our finding of 8 percent of people reporting sexsomnia seems really a high number, it should be stressed that we only studied patients referred to a sleep clinic. So, we would expect the numbers to be much lower in the general population."

Unfortunately, the survey revealed, sexsomnia does not seem to replace other symptoms of poor sleep.

Symptoms of insomnia, fatigue and depressed mood were similar between people reporting sexsomnia and other patients at the sleep disorders center, Chung and her colleagues explained in a statement.

But there was a hint of what might be behind the initiation of intercourse while dozing:

Both groups (sexsomniacs and other insomniacs) reported smoking and consuming caffeine at similar rates. But people who reported sexsomnia were twice as likely as other sleep center patients to admit using illicit drugs (15.9 percent vs. 7.7 percent).

Patients seem reluctant to talk about their late-night antics.

Patients rarely mentioned sexsomnia to their doctor, the survey showed. Only four of the 63 sexsomniacs in the study had complained about it during a consultation with a sleep specialist.

"It seems that patients generally don't discuss this with their doctors," Chung said.

Sexsomnia appears to occur predominantly during confused states of arousal, experts say, and it may occur during an episode of sleepwalking. Both disorders that are classified as "parasomnias," which involve undesirable behaviors that occur while falling asleep, during sleep or while waking up.