You know the drill when you're sleep-deprived: You'll just wait until weekend when you can hit the sheets early, then snooze until noon the next day. But even after all that rest, your brain still feels foggy in the morning. Why are you still so darn tired?

Allow science to explain: Your well-meaning attempt to log more Zs confuses the part of your brain that controls your body's daily cycle, better known as your circadian pacemaker. This group of cells clustered in the hypothalamus controls your hunger, thirst, and sweat. But since it's primarily triggered by light signals from your eyes, the pacemaker knows when it's morning and sends chemical messages to keep the rest of your body in check. So even though it's only 11 a.m., your cells started sucking up energy way before that. 

Scientists believe circadian rhythms evolved to help people adapt to seasonal changes, as well as their daily environment. Which explains why oversleep isn't just a bad idea on the weekend but also over the long term. A Harvard study recently cited in Wired found oversleeping won't just put you at risk for diabetes, heart ailments, and obesity--over time it can also damage your memory.

Harvard estimates oversleep affects about 4 percent of the population, mainly those who work odd hours, suffer from a sleeping disorder, or have an uncomfortable sleeping situation, perhaps resulting from surgery. Then again, for many people there are other issues to blame, such as drinking too much, taking drugs, or being depressed. None of these things are good on their own, but combined with oversleeping, they could have even more serious consequences.