A Austrian study found that if men sharing a bed with a bed mate it affects their mental ability the next day.
Although the men reported they had slept better with a partner, they fared worse in the tests, with their results suggesting they actually had more disturbed sleep.
Both sexes had a more disturbed night's sleep when they shared their bed.
But women apparently managed to sleep more deeply when they did eventually drop off, since they claimed to be more refreshed than their sleep time suggested.
Their stress hormone levels and mental scores did not suffer to the same extent as the men.
But the women still reported that they had the best sleep when they were alone in bed.
Bed sharing also affected dream recall. Women remembered more after sleeping alone and men recalled best after sex.
"Historically, we have never been meant to sleep in the same bed as each other. It is a bizarre thing to do.
"Sleep is the most selfish thing you can do and it's vital for good physical and mental health.
"Sharing the bed space with someone who is making noises and who you have to fight with for the duvet is not sensible.
More on BBC News: Bed sharing "drains men's brains"