Whether you feel hungover or well-rested after a night of sleep, it all comes back to a little thing called your circadian rhythm, according to Elite Daily.

Sleep is a beautiful thing, but believe it or not, it’s definitely possible to get too much of it. You know the feeling: You lie down in bed after a long day, and maybe you don’t really intend to sleep in that much, but by the time you wake up, you realize you’ve been asleep for 12 hours, and you feel like you just got back from a wild bachelorette party.

Your head is throbbing, your brain is foggy, and you’re completely out of it. You might not know why you feel hungover when you sleep too much, but you do know the feeling is real, and that it’s definitely not worth the extra hours of being wrapped up in your favorite blanket. So why does this happen, and how can you avoid it in the future?