Making love in the middle of the night sounds undoubtedly pleasurable.
But what if you suddenly realise that your partner is fully asleep on the job?
One couple in the UK related their story to the Daily Mail. The wife, Anita Sayer, 29, says she would wake up to her husband's urgent groping.
She has to push her persistent husband forcefully to the other side of the bed - and this can happen up to three times a night, leaving her annoyed and exhausted.
Her husband Dan always responds with a blank stare when she tells him about his fumbling in the wee hours of the morning: he simply doesn't remember.
He has what researchers term "sexsomnia."
First identified as a condition in the 90s, it collectively describes behaviours such as masturbation, fondling, sexual intercourse with climax and sexual assault or rape while asleep. And sexsomniacs don't recall any of their behaviour at all.
Brain gets "switched off"
Dr Matthew Walker, professor of neurology at the National Hospital for Neurology and Neurosurgery in London, says that an act of sexsomnia is most likely to occur in the first few hours of the night, during the deep sleep state.
"At this time, the cortex - the thinking, planning, awareness part of the brain - gets switched off. But the brain stem, the part responsible for the basic urges like the drive to eat or have sex, is still working.
"By this stage, the sexsomniac is acting completely without inhibition. And because the lower level of the brain is amnesic, he or she will have no memory of what he or she has done."
In a study done in Toronto, Canada, nearly 8 per cent of patients referred to a sleep disorder clinic reported that they had initiated or taken part in sexual behaviour while sleeping. Men accounted for three-quarters of the self-reported sexsomniacs.
"We were surprised at how common it was," said study author Sharon Chung, a staff scientist in the Sleep Research Laboratory at the University Health Network in Toronto. "We thought we'd get just a handful of people, yet it was almost one in 12."
Mr Sayer, a 24-year-old sales executive tells The Daily Mail: "I wake up and look at Anita and I can immediately tell from the look on her face I've done it again.
"But I honestly don't remember any of it and I don't like the fact that I am upsetting her, yet can't control it."
Other reported cases of sexsomnia include a woman in her 20s who would, while asleep, suddenly tear off her clothes and masturbate during the first half of the night.
If she were interrupted by her husband, the behaviour could happen once or twice again later in the night.
If awakened, she would refuse offers of intercourse and would deny that the behaviour had happened.
Sex with strangers
Sex with strangers
Another case reported by New Scientist magazine involved a middle-aged Australian woman who left her house and had sexual intercourse with strangers over several months.
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 Dr 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.
There are a number of examples in the research literature describing men having intercourse with their partners while asleep. Usually the women describe the man as being "glassy-eyed" and vacant. The behaviour stops if he is awakened.
Such behaviour seem to happen most often in people with other significant sleep-related problems, such as sleepwalking or driving and eating while asleep.
Other factors that may increase the risk of sexsomnia include the use of alcohol or sleep disruption caused by obstructive sleep apnea and sleep deprivation. But there are also detractors.
Happy ending for some
Mr Darren Greenwood, a 33-year-old window-fitter from London, was cleared of sexually assaulting a woman last year after he told jurors he'd suffered from parasomnia in the past, which involved sitting up in bed and punching a wall. Many believed it was too convenient an excuse.
But sexsomnia can have a far less sinister side.
Ms Dee Harris, 25, insists it is due to her husband Ryan's "dis-inhibiting" at night that they have their much longed-for son Lincoln.
The UK couple had been trying for a baby for 18 months and were about to launch into fertility treatment when Mrs Harris discovered she was pregnant.
"When I looked back, it was clear I'd conceived on the night we'd had "sleep sex", as we call it, which means when I'm half awake and Ryan is totally asleep."
This article was first published in The New Paper.