During his waking hours Tim Draper, 33, is a loving and devoted husband to his wife Amanda, 34.
But as soon as he falls asleep he turns into an aggressive sex-crazed 'monster' who gropes his partner before holding her down and ripping off her nightdress.
Builder Tim - who wakes up every morning with no memory of what he has done - suffers from a rare sleep disorder called sexsomnia.
Devoted wife Amanda Draper with her husband and sexsomniac Tim Draper
The Drapers, who live in Ontario, Canada, have been together 14 years and married for four. A night-vision camera was placed in the Draper's bedroom to record Tim's actions for a TV documentary. It shows Tim forcefully fondling his wife while she continually pushes his hand away.
Experts believe sufferers are driven by subconscious primeval instincts to mate.
Amanda - who frequently has to leave the marital bed in the middle of the night - explained: 'It happens about every other night and is really bad once a week.
'He has ripped my nightgown to the point where buttons have come right off and he has torn big holes in my under-clothing.
'He uses force to keep me down. It's scary. He doesn't hit me but I do get marks on my arms from him holding me down.
Devoted wife Amanda Draper with her husband and sexsomniac Tim Draper, who wakes up every morning with no memory of what he has done
'At first it was terrifying but I know it is not really Tim doing it. I'm almost used to it by now but I always wonder whether I'm going to get a good night's sleep.
'All the experts we have seen just shake their heads because they don't understand what is causing it.'
On being shown footage for the first time what he does in his sleep a shocked Tim said: 'It's painful. To me, that's just a monster. It's very extreme.
Tim Draper has a rare sleep disorder that means he tries to force his wife to have sex while he is asleep
'I feel bad that it happens. I have no idea what goes on. My body is doing what it wants without me having any control over it.
'It's like Jekyll and Hyde. I wake up without any notion of what I've done. I feel guilty about it but I also have no control over it. I really wish I did.'
Tim talks to a documentary crew about his experiences
Tim believes he has suffered from sexsomnia since his teens but was only diagnosed with the condition this year.
He cannot remember anything that happens during his sleep and only knows he has misbehaved if he wakes up to find Amanda asleep on the sofa in the lounge.
After watching the footage the following day, Amanda - who never lets Tim have sex with her in his sleep - says: 'I know it's not his fault and it's not him because I would not have married the person he is when he's sleeping.'
Doctors have prescribed Tim with a sedative called clonazepam, which is used to treat anxiety and insomnia and keeps him in a deeper state of sleep.
However, the drug has only made a slight improvement to curbing his nocturnal sexual activities.
Sleep Walkers: Secrets of the Night is on ITV1 at 9pm tonight