It’s been a long week at work, so Friday night, you do the sensible thing by going to bed early and sleeping in with the view of waking up feeling fresh and energized. But when you wake up the next morning your body feels heavy, your brain is still lying down and you even have faint headache. If too little sleep is a problem, then why is extra sleep a terrible solution?
Oversleeping feels so much like a hangover that scientists call it sleep drunkenness. It makes you feel sluggish by confusing the part of your brain that controls your body’s daily cycle. Your internal rhythms are set by your circadian pacemaker, a group of cells clustered in the part of the brain that also controls hunger, thirst, and sweat. Primarily triggered by light signals from your eye, the pacemaker figures out when it’s morning and sends out chemical messages keeping the rest of the cells in your body on the same clock.
Scientists believe that the pacemaker evolved to tell the cells in our bodies how to regulate their energy on a daily basis. When you sleep too much, you’re throwing off that biological clock, and it starts telling the cells a different story than what they’re actually experiencing, inducing a sense of fatigue. You might be crawling out of bed at 11am, but your cells started using their energy cycle at seven. This is similar to how jet lag works.
But oversleep isn’t just going to ruin your Saturday hike. If you’re oversleeping on the regular, you could be putting yourself at risk for diabetes, heart disease, and obesity. Harvard’s massive Nurses Health Study found that people who slept 9 to 11 hours a night developed memory problems and were more likely to develop heart disease than people who slept a solid eight.