Why do guys get sleepy after sex?

Is it insensitivity when a guy falls asleep right after sex? This article talks about the chemical reasons why guys might feel sleepier. Well, I guess everybody's different, but no matter how much science you hand me, if I have a choice between a guy who says he loves cuddling afterwards and a snorer, my biology's gonna be all over the first guy.

NYU (the home of the blog where this aricle appears) accompanies the story with a photo of a full-frontal-nudity sculpture from 200 B.C. Just look at the pecs on that guy...