Is it possible to have sex while fully asleep? Canadians researchers say yes and that it happens a lot more frequently than many may have thought.

Toronto researchers say their research at a sleep disorders centre found that 7.6 per cent of patients engaged in sexsomnia, initiating or engaging in sexual activity with a partner while asleep.

The rate was nearly three times higher in men than women -- about 11 per cent in men, and 4 per cent in women.

The researchers want to make it clear that while those numbers sound quite high, it should be stressed that they only studied patients referred to a sleep clinic.

"So, we would expect the numbers to be much lower in the general population," noted one of the study's co-investigators, Sharon A. Chung, a Sleep Research Laboratory staff scientist in the department of psychiatry at the University Health Network in Toronto.

The researchers say this is the first study to examine the prevalence of sexsomnia among those suffering from sleep disorders.

Chung's team reviewed charts of 832 patients who suffered from suspected sleep disorders. The 428 men and 404 women filled out questionnaires about their symptoms, behaviours during sleep, fatigue and mood.

They found that almost 8 per cent of the patients suffered from sexsomnia. The disorder left them with fatigue, insomnia and depressed mood.

It's not known what causes sexsomnia, but it's thought that fatigue and sleep deprivation are factors, as are alcohol consumption and stress.

While those patients reporting sexsomnia reported similar rates of smoking and caffeine consumption as other patients at the sleep disorders centre, "sexsomniacs" were twice as likely to admit using illicit drugs (15.9 per cent vs. 7.7 per cent).

The researchers also found that while sexsomnia was relatively common, patients rarely mentioned the problem to their doctor.

Chung noted that only four of 832 patients expressed a complaint about sexsomnia during a consultation with a sleep specialist.

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

The research was presented Monday at SLEEP 2010, the 24th annual meeting of the Associated Professional Sleep Societies in San Antonio, Texas. The research has not yet been published or peer-reviewed.

According to the International Classification of Sleep Disorders, published in 2005 by the American Academy of Sleep Medicine, sexsomnia appears to occur predominantly during "confusional arousals" and may occur during an episode of sleepwalking.

"Confusional arousals" usually happen without the sleeping person coming to consciousness. If the person isn't woken during the event, they usally have no memory of it happeaning.

Sexsomnia can be treated, often by treating the cause of the sleep disturbances. That might mean eliminating alcohol or drugs, or avoiding shift work.

Some patients also suffer from sleep apnea, and when that condition is treated, the sexsomnia ends. There are also medications available, such as bedtime benzodiazepines.

One of the most well-known cases of sexsomnia in Canada involved a man named Jan Luedecke, who was charged with sexually assaulting a woman at a 2003 house party in Toronto.

He was found not criminally responsible after court heard testimony that Luedecke suffered from sexsomnia.

Four previous girlfriends testified that Luedecke had engaged in "sleep sex" with them prior to the assault. He also testifed that the day before the assault, he had taken magic mushrooms and had been drinking heavily in the hours leading up to the assault. He was also overworked, stressed and sleep-deprived, which are believed to be triggers for sexsomnia.

The trial judge acquitted Luedecke on the grounds the he could not have formed the intent to commit the assault, while also concluding that his condition did not qualify as a "disease of the mind."