There's an actual scientific reason why a lot of men fall asleep after sex - and it's all to do with your brain chemicals.
Considering the vast majority of sex takes place in bed, it's understandable that the body would associate this with sleep.
And let's be honest most couples tend to have sex either at night or maybe in the morning if you're lucky. Both of these are times where you're just more likely to be naturally tired.
However, Melinda Wenner, of Scienceline, told Live Science that there is actually far more at play here than just mere object association and time.
During sex the brain releases a cocktail of brain chemicals, including norepinephrine, serotonin, oxytocin, vasopressin, nitric oxide (NO), and the hormone prolactin.
Prolactin is linked to the feeling of sexual satisfaction, and is also the cause of the 'recovery time' before men are ready to go again. Prolactin levels tend be higher during sleep, as well as during sex.
Prolactin may also explain why men often become sleepy after partnered sex but not after masturbation.
An orgasm during sex with a partner releases four times as much prolactin than a solo orgasm, though scientists aren't quite sure why that is.
Oxytocin and vasopressin, which are both released during orgasm, are associated with sleep too.
Their release frequently comes alongside the release of melatonin, the hormone that regulates the body clock.
Similarly, PET scans have discovered that in order to reach orgasm one must release all fear and anxiety, which can also cause sleepiness. So if you're reaching orgasm, they chances of feeling sleepy after sex may increase.
Studies suggest that women are less likely to fall asleep immediately after sex, even if they do reach orgasm. Following sex, women are more likely to stay semi-aroused while men need a 'recovery period'.
One argument as to why this affects men more than women is that the exertion of having sex tends to reduce energy-producing glycogen in muscles, the Times of India reports.
Women, on the whole, have less muscle mass than men meaning they will be less likely to feel tired afterwards.
Well whatever the reason ultimately is, it's certainly something that affects huge swathes of men.
And if you have fallen asleep after sex, at least that's better than falling asleep during the act.
One study even found that of 1,000 men 48 percent said they have fallen asleep during sex.
Featured Image Credit: AlamyTopics: Sex and Relationships
Isobel Pankhurst