Why You Fall Asleep within Minutes of Having Sex

There’s a common nighttime occurrence 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 Health sleep 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.

But what if you don’t want to feel tired afterward?

Maybe you’d like to stay up for a bit with your partner. 
Or maybe you just finished a mid-day romp, and you want to seize the day afterward (or at least be a functioning human being, and not a zombie). 
Then make sure you pick a sex position that’s not horizontal, says Dr. Winter. Sure, it obvious, but lying on your back signals to your body that it’s time to sleep.
Luckily, you can find tons of non-prone ways to do the deed in The 45 Best Sex Positions for Couples.
You should also keep the lights on. That way, you won’t kickstart your sleep cycle, he says. 
And get out of bed once you’re finished. Over your lifetime, your brain has come to associate the bed as a location for dozing. It’ll be nearly impossible to fight the urge to hit the hay if you just lie there quietly. So no snuggling allowed.