Why men sleep immediately after having s*x.

There’s something common happening in bedrooms around the world: After sex, men fall into a deep sleep, while women everywhere lay awake silently cursing their snoozing partner’s name. 

You can thank the hormone prolactin for your male post-coital sleepiness, says Men’s Healthsleep advisor W. Christopher Winter, M.D. 

Prolactin suppresses dopamine—a stimulating neurotransmitter that makes you feel
 awake, he explains.  

And your body releases it in spades when you come. Your wife’s body, however, doesn’t produce nearly as much, says Dr. Winter.

But prolactin isn’t the only reason you can’t keep your eyes open. 

The “feel-good” hormone oxytocin also surges during sex, which can vanish any stressful thoughts from your mind, making it easier to relax and fall asleep afterward.

And if you have sex with the lights out, you’ll signal to your body’s internal clock that it’s time for bed. When that happens, the hormone melatonin ignites your sleep cycle. 

When prolactin, oxytocin, and melatonin all come together, you have the trifecta for a fantastic snooze. also

Dr Stoléru explained: “After men have an orgasm they usually experience a refractory period when they cannot be aroused.

"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.