Sleep myths and facts

Napping is a bad habit
Napping is a complex issue -- depending on the situation, a nap can be either helpful or harmful. The major factor to consider is what effect a nap will have on your main sleep block. If it's likely to curtail it, then napping is inadvisable, since ideally you want the main sleep period to be as long as possible. If a nap is unlikely to affect the main sleep block, then it's perfectly okay.

"Bad" naps come up most often in the context of people with chronic insomnia. These people often get less than six hours of sleep at night, leading them to feel sleepy during the day. Giving in and taking a nap--especially a long one--only perpetuates the cycle of nighttime insomnia and daytime sleepiness. In such cases, the individual needs to pinpoint the source of the insomnia and address it (see Chapters 8 and 9).

The timing of a nap can also affect its desirability. If you keep traditional hours, it's generally a bad idea to nap in the evening, since this makes it harder to fall asleep at night. Unless your safety is in danger and you need the nap to stay awake for the next few hours, you're usually better off toughing it out until your regular bedtime.

In most other situations, though, naps are beneficial. For example, if you don't have insomnia but experience an occasional night of short sleep (from work stress, noisy neighbours, child care demands, and so on), then a nap is a great way to replace your lost sleep. Many people whose sleep is curtailed by the morning alarm clock routinely squeeze in a short afternoon nap, and this is healthy. Naps are also a lifesaver for shift workers, due to the sleep deprivation that frequently accompanies working at night (see Chapter 16).

It's possible to get too much sleep
You've probably heard people say that if they sleep too much they feel tired when they wake up. This is a misconception. First, you can't get more sleep than your body needs. The homeostatic drive to sleep wears off as you sleep and stops exerting its pressure. In the morning, the circadian cycle is in its alert phase, not its sleep phase. So if you continue to sleep, it's because you need more sleep.

Second, the grogginess that some people report with longer sleep isn't due to the extended sleep. Most often, people extend their sleep because they've been depriving themselves for several nights. A single night of extended sleep does not make up all of the sleep debt, so when they wake up, they're still sleep deprived and as a result don't feel refreshed.

Finally, if you extend your sleep into the afternoon you may wake up at a time on your circadian clock when it's natural to be sleepy, which may contribute to that groggy feeling.

Don't let fear of feeling bad keep you from getting enough sleep. Listen to your body; it will tell you whether or not you need more sleep. If you're sleepy, you need more sleep.

How I sleep doesn't affect the rest of my health
More and more evidence is accumulating showing that overall health is very much tied to sleep quality and quantity. Specific sleep disorders, such as sleep apnea, can cause heart hypertension and heart disease. Mood and mental health are affected by sleep. Sleep deprivation is linked to the development of obesity, diabetes, and heart disease and can even affect your life span. So give sleep its due.

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Excerpted from The Harvard Medical School Guide to a Good Night's Sleep by Lawrence J. Epstein, M.D., with Steven Mardon. Excerpted by permission of McGraw-Hill. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.