Waking up can be hard to do. The idea of work trumping sleep is insane. The only thing to get you up and going is usually coffee. Oh, and sex.

People can feel extremely horny in the morning. Men, for instance, are known for waking up with hard-ons without even consciously thinking about sex. But what about women?

Having a vagina and getting “morning wood” doesn’t sound right. But women can actually wake up with it, too. They get increased clitoral and vaginal engorgement. The big difference is that, while for men it’s an extremely visual outcome, it happens internally for women. This is why most women aren’t even aware of the process. And why they can’t wrap their heads around why morning sex is so damn good.

As a woman goes through the REM sleep cycle, the body pumps blood full of oxygen to the genital tissues to keep her sex organs healthy. This is the same process that occurs when a woman becomes aroused. The clitoris’ erectile tissue becomes swollen and red with increased circulation and a faster heart rate. The labia can also become engorged and deeper in color, and the vagina can become more lubricated.

Morning wood—both for men and women—isn’t, therefore, always due to arousal. Sometimes it’s just a biological process occurring. But the point is that, despite how grumpy she might be in the morning, your girlfriend is probably horny and you should probably take care of her.

Maybe that’s why she’s grumpy after all.

Photo: iStock/PeopleImages