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MYTH: Your body and brain shut down for rest and relaxation when you sleep.


FACT: Some physiologic processes actually become more active when you sleep; for example, secretion of some hormones increases, as does activity of the brain's pathways for learning and memory. No evidence supports the hypothesis that any major organ (including the brain) shuts down during sleep.


MYTH: Sleeping 1 hour less per night than you need won't affect your daytime functioning.


FACT: Even slightly less sleep can impair your ability to think clearly and respond quickly, although you may not be noticeably sleepy during the day. Not getting enough sleep also can compromise your cardiovascular health and immune system. If you consistently fail to get enough sleep, you'll eventually become excessively tired during the day.


MYTH: Your body adjusts quickly to different sleep schedules.


FACT: Most people can reset their biological clock by only 1 to 2 hours per day. It can take more than a week to adjust to a dramatic change in your sleep-wake cycle, as happens when you travel across several time zones or switch from working day shift to working night shift.


MYTH: If you're excessively tired during the day, extra sleep at night is the cure.


FACT: With sleep, quality is as important as quantity. If the quality of sleep is poor (for example, because of a sleep disorder or medical condition such as obstructive sleep apnea), even sleeping 8 or 9 hours won't refresh you. Make behavior changes or get treatment as needed to address underlying disorders that disrupt sleep.


MYTH: Sleeping more on the weekends can help you make up for sleep lost during the week.


FACT: Sleeping in can help ease part of a sleep debt, but it won't erase it completely, and it won't affect performance impaired during the week because of inadequate sleep. Also, sleeping in on weekends can affect your biological clock, making it harder to go to bed at the right time Sunday night-and even harder to get up early on Monday morning.


MYTH: Children who don't get enough nighttime sleep will be sleepy during the day.


FACT: Unlike adults, children who don't get adequate sleep become more active than normal during the day. They also have difficulty paying attention and may be misdiagnosed with attention-deficit hyperactivity disorder.


MYTH: Worry is the main cause of insomnia.


FACT: Worry can cause a short bout of insomnia, but a persistent inability to fall asleep or stay asleep can be caused by various medications, sleep disorders, and health problems such as depression, anxiety, asthma, or arthritis. Sometimes, people with chronic insomnia appear more active than normal, making it harder for them to fall asleep.


Source: U.S. Department of Health and Human Services, National Institutes of Health, National Heart, Lung, and Blood Institute, Your Guide to Healthy Sleep, NIH Publication No. 06-5271, November 2005.