I mean, obviously…
It makes women sleepy, too.
It is just the release and relaxation that results from orgasm.
Do we really need research on this?
LINK TO COLUMN: http://www.straightdope.com/columns/read/1140/why-do-men-feel-sleepy-after-sex
Are you asking for volunteers?
The phenomenon is more likely to occur when an individual takes a resting position immediately after orgasmic sex. It more often manifests in male individuals than in female because of differences of innervation by sympathetic and parasympathetic ganglia of the autonomic nervous system during sexual intercourse.
For female subjects, in the moments prior to orgasm, sensory stimulation is under the influence of the parasympathetic ganglia. At the moment of orgasm control suddenly switches to the sympathetic ganglia. This causes a transition of from deeply relaxed and happy to amazingly excited and happy.
For male subjects, the exact opposite is true. Prior to orgasm, sensory stimulation is under the guidance of the sympathetic nervous system. At the moment of orgasm control suddenly switches to the parasympathetic ganglia. If the orgasm is immediately followed by a physical state of rest, parasympathetic rebound is likely to occur. This sends the subject into a deep state of relaxation often resulting in sleepiness and happiness.
Hmm. The original column was from 1995, sounds like there’s been some advances in the last 20 years. I’ll put your info before Cecil, timmZero, and see if it’s time for an update.
There are a couple of grammatical errors. I was unable to edit post-posting, for some reason.
Posts here may only be edited within 5 minutes.
If the errors are serious (f’rinstance, if you typed “now” instead of “not”), email a Moderator and we’ll be glad to fix 'em for you. Otherwise, we’ve all just learned to be more patient with other people’s tpos.
At the strictly anecdotal level, most of the women I’ve made love with needed/wanted a nap worse than I did by the time we were done. I’ve never (that I remember) made love with someone and had them perk up and chat. Women I’ve been with generally want to be held afterwards, but they’re ready for some rest.
You must read a different board than the rest of us.
Oh, and *typos. 
You think that wasn’t deliberat?
In the only case I know of, (mine) no it does not, in fact much like drinking, it makes me much more energetic than I was before sex.
I know…weird.
This is usually the case with me too.
After an orgasm, I usually feel sleepy – never energetic. In fact, there have been plenty of times that I’ve used it as a way to help me fall asleep and it worked quite well. In the afterglow, those feel-good chemicals are coursing through my veins and I feel very relaxed. Often I fall asleep even if it’s the middle of the day and I was fighting to stay awake. But I might only fall asleep for a few minutes. When people say orgasms make them feel energetic, I just scratch my head in disbelief; it’s totally outside of my experience.
As per sbunny8, the feel-good chemicals are coursing. If I reset and don’t move around, the continue to do their job longer and yes, I feel sleepy. If I start moving around, my body seems to flush them away rapidly.
Ya know, if people are going to share their personal anecdotes, that’s great. But given the subject, they might consider not leaving their gender ambiguous in order to at least give the anecdotes *some *value. Just sayin’…
so you were faking it?
I know I’m not supposed to gush, but that was a particularly funny column of Cecil.
There’s nothing wrong with gushing. It’s common for a lot of women, and can be a very satisfying form of release.
Just be sure to wipe your keyboard and mouse off afterwards.