Apparently, Guys Fall Asleep After Sex

Yeah, I do get sleepy (and to head off the obvious jokes: sex with women. Many, many women). I get so sleepy in fact, that I sometimes think about doing research, but fall asleep before getting it done (and after getting it done, if you know what I mean... sex... with women). Mental Floss did the work for us and explains the phenomenon. One, often sex is had at night and in bed. So not only are you tired because of the time, you're also tired from the extra physical exertion and because you're in a comfy, soft place (i.e. the bed... get yo' head out the gutter). Also, you don't properly regulate your breathing when you're doing the horizontal mambo.

Most interesting is the chemistry involved in orgasm:

There’s also the biochemistry of the orgasm to consider.  After sex, a man’s brain releases a slew of hormones and neurotransmitters. Some of them, like prolactin, oxytocin and vasopressin, have been linked to sleep as well as sex. Prolactin plays a role in sexual satisfaction by counteracting the effects of dopamine** (which is responsible for sexual arousal). It’s also been shown that the artificial delaying of an REM sleep period disrupts the rhythm of prolactin release, and that REM sleep is reduced in mice with prolactin deficiencies. Oxytocin and vasopressin have also both been implicated in the body’s regulation of sleep cycles. While none of these chemicals are fully understood and their links to sleep aren’t concrete, the circumstantial evidence suggests that they may play a part in pulling you off to a post-coital snooze.

The writer explains that there's less definite explanations about why women don't get sleepy as much. Might be because they orgasm less. Good thing I have that "...Runs So Deep, Put that Ass to Sleep" diploma mounted on my wall (check the 3-minute mark in the vid).