Anecdotally, you know that not getting enough sleep leaves you feeling groggy and irritable. But studies show that over time, this effect is cumulative, with brain function decreasing day by day with no sign of leveling off. How long it takes to bounce back from this sleep debt depends on how long you've been deprived. A few late nights or early mornings can be counter-acted by just one or two more restful nights, but prolonged sleep deprivation takes much longer to recover from. And years of habitually under-sleeping could cause permanent damage.

What about people who claim to do just fine on just a few hours of sleep? It turns out that even though your cognitive abilities are on a steady decline, how tired you feel will eventually level off. Meaning, people who suffer from chronic sleep deprivation may have lost their ability to tell just how tired they really are.

The optimal sleep duration is between seven and eight hours a night. Any less is not only bad for your mental abilities but also increases your risk for heart disease, obesity and diabetes. Any more might not be bad for your brain, but oversleeping presents its own health risks. Find out more in the latest video from ASAPScience: