What Guys Said 1
He was probably still tired from the day before. I've fallen asleep in the middle of masturbating before lol so I'm sure it can also happen during sex. I think the difference between men and women is that if a woman is tired she'll say she is too tired for sex but if a guy is too tired he'll try it anyways.
What Girls Said 1
Us girls (and guys) are raised to think that all men are complete horn dogs that can't control themselves around a sexy and willing woman. This is not true at all! Guys get tired, stressed, sick, and some just don't have much of a libido (I'm dating one with no libido right now and went through the exact same thing as you when we went to Vegas! so your question made me smile). I promise you that him falling asleep had nothing to do with your looks, he was probably just exhausted from an active vacation. Do realize that while women can have sex for hours and hours, it takes a lot of energy as a man. If anything you should be happy that he wants to spend time with you with or without sex. :)