Abnormal sexual behaviour during sleep may be more common than thought, a review suggests.

The finding is in Sleep and Sex: What Can Go Wrong, a review of literature by Dr. Carlos Schenck of the University of Minnesota and his colleagues that is in Friday's issue of the journal Sleep.

The review covers sleep-related disorders, abnormal sexual behaviours and experiences known as sleepsex or sexsomnia.

"It seems that more and more reports are surfacing of abnormal sexual behaviours emerging during sleep," Schenck said. 

"While people may think this type of behaviour is humorous, in reality it can be disturbing, annoying, embarrassing and a potentially serious problem for some individuals and couples," he added in a release.

The behaviours included sexual vocalizations, violent masturbation that may leave bruises, fondling, intercourse and aggressive sexual behaviour during sleep.

People with sexsomnia often had other sleep disorders, such as sleepwalking, sleep apnea and sleep tremors. The behaviours often coincided with unusual brainwave patterns and short interruption in sleep, as in sleepwalking.

The search turned up more than 125 cases dating back to 1986 that provide the basis for a new classification system, the study's authors said.

Sleep sex has also been used as a defence in sexual-assault cases in Canada, the United States and Europe.