Sleep medicine experts have successfully treated a rare case of a woman having sex with strangers while sleepwalking.

The behaviour had disrupted the lives of the woman and her partner. At night while asleep, the middle-aged sleepwalker – who lives in Australia and cannot be identified for reasons of confidentiality – left her house and had sexual intercourse with strangers. The behaviour continued for several months and the woman had no memory of her nocturnal activities.

Circumstantial evidence, such as condoms found scattered around the house, alerted the couple to the problem. On one occasion, her partner awoke to find her missing, went searching for her and found her engaged in the sex act.

“Incredulity is the leading player in cases like this,” says Peter Buchanan, the sleep physician at the Woolcock Institute of Medical Research in Sydney, who handled the case. But a combination of factors convinced him that the case was a real sleepwalking phenomenon, including the distress of the couple, and an in-depth clinical evaluation.


Sleep talking

During that evaluation, the patient was assessed by psychiatrists, and checked for physical problems such as brain tumours, which may cause unusual behaviour. Neither of those examinations could find a cause.

However, she was found to have a history of talking in her sleep as a teenager and when monitored in the sleep laboratory, she was found to have a higher number of arousals from deep sleep than is usual. Both of these factors might indicate a susceptibility to abnormal sleep behaviour.

However, Roger Allen, a sleep specialist in private practice in Brisbane is sceptical. “Sex is a primal behaviour so it’s not impossible – men have erections in their sleep after all – but this case involved such complex behaviour it seems less likely.” He also points out that eliminating psychiatric conditions as a cause of the behaviour would be difficult.

Sleep driving

But there are some extraordinary cases of sleep walkers leaving their homes, driving cars, or engaging in behaviours that they would not usually. In 1987, Ken Parks, drove 23 kilometres from his home in Pickering, Ontario, to his in-laws house, where he strangled his father-in-law unconscious, and stabbed his mother-in-law to death. He was acquitted of murder because he was sleepwalking at the time.

“People in a state of automatism don’t have access to their full range of beliefs and desires, so it seems justifiable to excuse them,” says Neil Levy of the Centre for Applied Philosophy and Public Ethics at the University of Melbourne.

Sleepwalking is often triggered by stress, and this may have been the case with the Sydney woman, says Buchanan. She stopped her night-time excursions after psychiatric counselling. Drugs such as benzodiazepines, which are sometimes used to treat sleep walkers, were not necessary.

Any type of sleepwalking is rare. It occurs in around 3% of children and young adolescents, and about 0.5% of adults. Usually it involves little more than walking around in a fairly purposeful way while asleep, although sleepwalkers may lash out if awoken.

The results were presented at a sleep conference in Sydney on Friday.