Imagine finding unexplained condoms around your house and then waking up one night to find your partner having sex with a stranger.
It might sound like an affair, but what if your "cheating" partner was fast asleep during the act?
This is a condition completely distinct from sleepwalking and is a form of sleep disorder called REM behavioural disorder.
Normally, when a person enters a phase of sleep called the REM (rapid eye movement) phase, in which we can often dream, our bodies are immobilised.
In the case of sleep sex, this doesn't happen and the person can act out their dreams.
He said if what the person was acting out fitted with the dream they might not wake up.
"If you are lying there dreaming about having sex with your wife and you just happen to be having sex with your wife then there's nothing there to stop the dream. You don't perceive that as wrong."
clipped from: news.bbc.co.uk