14 of the biggest myths about sleep, debunked

• Until recently, scientists had trouble answering the question: why do we sleep?
• Now we know that sleep restores the immune system, body, and cleanses the brain.
• But there's still a lot we get wrong and don't understand about sleep. The longstanding lack of knowledge has created a lot of sleep myths.

For something so fundamental to our lives, there's a lot that we don't get right about sleep.

Until recently, we didn't even have good answers to the question of "why" we sleep, as UC Berkeley neuroscience and psychology professor Matthew Walker explains in his recent book, "Why We Sleep: Unlocking the Power of Sleep and Dreams."

We're better at answering that question now. We know that sleep restores the immune system, balances hormone levels, lowers blood pressure, cleanses toxins from the brain, and more.

"[W]e no longer have to ask what sleep is good for," wrote Walker. "Instead, we are now forced to wonder whether there are any biological functions that do not benefit by a good night's sleep. So far, the results of thousands of studies insist that no, there aren't."

But while we know far more about sleep now than we used to, there are a huge number of myths about sleep that persist. Many of these stem from not understanding the full importance of sleep; other myths have been created by people trying to sell products to improve nightly rest.

These are some of the most prominent myths - and the facts.