Every day almost every person on earth sleeps, yet many questions remain about this state of suspended consciousness and what it actually accomplishes.
We still don't know why we need shut-eye every night, just that we do.
Different myths and explanations have sprung up about all aspects of sleep, from dreams to what it is our bodies do when we're not conscious.
Many aspects of sleep are individual. We differ in the amount of sleep we need and in what can either help us drift off or keep us awake in the late-night hours.
Learning a little more about sleep might help you set up your own tests to see what works and what doesn't.
Here we explore some of the most common myths about sleep in the hope that the answers might lead you to a good night's rest.
Eight hours has long been touted as the gold standard of sleep time, but this number is an average: Most people need seven to nine hours. Some can get by on four hours a night, but others need as many as 12.
"We don't have a lot of data on what exactly the best amount of sleep for a person is, but it's most certainly individual," said Dr. Robert Basner, director of the sleep center at New York-Presbyterian Hospital/Columbia University Medical Center.
While there's a general idea of how much sleep a person needs, the specifics are less clear, and the advice given to determine the adequate amount of sleep can be misleading.
Here's a common suggestion for determining how many hours of sleep you need: How long do you sleep when on vacation, when an alarm clock is not waking you up because of work or other obligations?
But, Basner explained, the number one would get from that is likely to be too high, because we deprive ourselves of sleep beforehand.
"Most people in our society would be making up for lost sleep time," he said.
So trial and error may be the only good method for the average person.
"We don't have any kind of test," said Philip Gehrman, clinical director of the behavioral sleep medicine program at the University of Pennsylvania. "I often say to my patients that if you don't feel fully rested during the day, then you need more."
The majority of people who claim to need next to no sleep seem to have a lack of self-awareness rather than a superior ability to function.
"There's very few people who can consistently get less than four hours of sleep and function during the day," said Gehrman, noting that people who can get by on six or fewer hours are known as "short sleepers."
He noted that when many people who claim not to sleep during the night are observed in a sleep lab, parts of their brain shut down, so although they are no longer fully conscious, they might believe they are.
Basner has made similar observations about people who claim they need or get almost no sleep.
"If someone is functioning well ? and they say they're sleeping one to two hours, they're probably sleeping longer," he said.
Some people can function on very little sleep, but it is unclear whether they'd function better if they allowed themselves to get more.
"Getting by and functioning optimally are two different things," said Basner. "The preponderance of evidence would be anyone sleeping less than three hours is not going to be getting enough sleep and functioning as best as they could."