It is no secret that many men nod off straight after sex. And for their female partners, the loud buzz of snoring after a passionate encounter is practically guaranteed to sour the mood.
But now scientists might well have given men the perfect excuse for feeling drowsy: they just can't help themselves.
Experts conducted research which involved scanning the brains of men during and after orgasm.
In the case of the latter, they found that the cerebral cortex - which plays a vital role in attention, consciousness and perceptual awareness - shut down almost immediately after orgasm.
Serge Stoleru, a French government scientist, said that the research offers the 'first hints' of what happens in the brain during sex.
He told the Sunday Times: 'For women, it seems to be different. 'They don't seem to have such a strong refractory period and may be asking for more when their partners just want a rest.'
The study also showed that the brain switched off almost all sexual desire after orgasm.
And as well as this, men have a further reason for feeling drowsy: their brains become flooded with sleep-inducing chemicals such as serotonin after they have had sex.
Earlier studies have also suggested that men aren't to blame for wanting to take a well-earned break after sex.
In 2005, research found the blood rush after climax depletes the muscles of energy-producing glycogen.
And because men typically have higher muscle density than women, they become more tired after sex.
Dr Neil Stanley, director of sleep at the University of Surrey, said that men were not completely at fault.
'As frustrating as it is for most women that their male partners just roll over and fall asleep after sex, men aren't entirely to blame,' he said. 'Humans are the only animals in which sleep and sex are linked and while often seen as just a poor excuse, there are scientific reasons why men feel tired after sex.'
The survey showed the majority of men did feel more relaxed straight after sex.
Eighty percent of men said they felt able to drift off without any problems after making love, compared with just 46 percent of women.
They were amongst 10,000 adults surveyed by organisers of The Vitality Show, Europe's largest health and beauty exhibition.
The survey also found 48 percent of men had actually fallen asleep during the act itself.
And whilst scientists might have rescued men from a telling off for sleeping straight after orgasm, it seems perhaps understandable that the latest research won't do the same for those who doze before reaching climax.