There is no single, definitive scientific explanation for this age-old conundrum. But if you think about it long enough, the s*x–sleep connection makes sense, particularly when you consider that many men have their first orgasms while unconscious. Wet dreams, nocturnal tumescence, morning erections…When all is said and done, we may not be much better than praying mantises: The males keep copulating even after they’re decapitated by their lovers.
After climax, both men and women release the chemicals oxytocin, prolactin, gamma amino butyric acid (GABA), and endorphins. Each of these contributes to that roll-over-and-snore feeling. The hormone oxytocin is known to have several effects, including establishment of maternal behavior, stimulation of uterine smooth-muscle contraction at birth, and stimulation of milk ejection (milk letdown). It is also referred to as the “cuddling hormone” because it tends to elicit the need to be close and bond. In one study, oxytocin was shown to inhibit male s*xual behavior in prairie voles. Maybe it’s the oxytocin that makes us feel satiated and rested.Prolactin is another player in the s*x/sleep saga. It is produced in the pituitary gland, and its best-known function is the stimulation of milk production. Prolactin is believed to relieve s*xual arousal after climax and take your mind off s*x. Levels of prolactin rise during sleep, and some patients with prolactin-secreting tumors report sleepiness. So prolactin seems like it may be a culprit.GABA and endorphins also both have a calming effect and may make you pass out after s*x. So why does the postcoital snooze seem to be so much more a man thing?This may come as quite a shock to some of you, but men are known to release in various semicomatose states, such as during prostate exams and while thumbing through dog-eared issues of National Geographic magazine, women—believe it or not!—don’t always have orgasms during s*x, and that keeps them from producing all those other hormones.