London - Groaning during sleep is much more common than previously thought, say researchers from the University of California, but goes under-recognised as it can be confused with snoring.
The condition, also known as catathrenia, is louder, occurring on exhaling, causing the vocal cords to vibrate, while snoring usually happens when you inhale.
Groans can last up to 50 seconds and occur many times a night.
As well as embarrassment, it can cause fatigue and depression in sufferers (typically male) and their partners.
Yoga or exercises for the facial muscles might help and should be further investigated, the researchers said.