Why do men fall asleep after sex?

Co-authors Mark Leyner and Dr. Billy Goldberg give answers to questions ranging from the bizarre to the slightly embarrassing in "Why Do Men Fall Asleep After Sex," their follow-up book to their No. 1 New York Times bestseller, "Why Do Men Have Nipples?"

From questions about dogs' belly buttons to knocking down old wives' tales — no question is too weird for this duo.

Question: So you put it out there — and we've got to ask: Why do men fall asleep after sex?

Leyner: People have no idea how much work it is for a man to produce an ejaculation. You have this seminal vesicle churning out this fluid, the prostate gland producing an alkaline solution. It's like having five iron chefs in your crotch working to cook up this stuff.

Goldberg: There are hormones that are secreted at orgasm — proloactin, oxytocin —that facilitate sleep. But you have to accept as gospel that men orgasm more than women. If that's true, then you have your answer as to why men fall asleep after sex. …And it seems like women don't. If women orgasm as much as men, we might all be asleep all the time.

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