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updated 2/12/2010 11:18:58 AM ET 2010-02-12T16:18:58

Our bodies give us plenty of signals when we're tired, but some of us are so used to being sleep deprived that we remain oblivious to how impaired we really are. Sleep debt isn't something you can pay off in a weekend, researchers say — it can take weeks of building up restorative sleep habits. In the meantime, here are some signs you might be sleep deprived, and temporary fixes while you get your sleep schedule back on track.

1. YOU'RE FLUMMOXED BY EVEN SIMPLE DECISIONS

You're up late one night booking your next vacation, and even though you know the dates and destination, you're overwhelmed by minor details. Should you get a refundable ticket? Window or aisle seat? Rent a car now or later? When you're tired, you're less able to distinguish between important and irrelevant information, such as your seat assignment, according to Sean Drummond, PhD, a sleep researcher at the University of California, San Diego. The result: Even the simplest decision takes on exaggerated importance.

Tired people also take riskier gambles to maximize results (Maybe if I wait until the last minute, the ticket price will go down) and have trouble adjusting to changing circumstances (like firming up an itinerary if flying from an unfamiliar airport).

2. YOU'VE BEEN EATING ALL DAY, AND YOU'RE STILL HUNGRY!

Studies show that chronic sleep loss can disrupt blood sugar levels and cause the body to produce less leptin, a hormone that curbs appetite, and more ghrelin, leptin's hunger-stimulating counterpart. Because of these physiological changes, you may be more likely to overeat when you skimp on sleep — and the food you pick probably won't be either nutritious or a lasting source of energy. Tired people tend to be particularly drawn to sugars and other simple carbohydrates, probably because the body is looking for a quick pick-me-up, says Lisa Shives, MD, a spokesperson for the American Academy of Sleep Medicine. Sleep deprivation also tends to erode self-control, making you more likely to choose a brownie over carrot sticks.

3. YOU KEEP COMING DOWN WITH COLDS

People who get inadequate sleep are more vulnerable to infection than those who are well rested, says William Kohler, MD, medical director of the Florida Sleep Institute. In one study, researchers injected healthy volunteers with a cold virus. Those who slept less than 7 hours a night for the previous week were 3 times more likely to develop symptoms than those who got 8 hours or more. In another study, people who got only 4 hours of sleep for several nights in a row had a weaker immune response to the flu vaccine than those who slept between 7-5 and 8.5 hours.

Cold front: The top 10 worst things for your immune system.

4. THE BALLADS ON AMERICAN IDOL MOVE YOU TO TEARS

Don't automatically chalk up your sudden weepiness to PMS: Without sleep, you are more emotionally volatile. In one brain-imaging study, for example, people who missed a night of sleep and viewed disturbing images had 60% more activity in the amygdala, which is involved in processing fear and anxiety, compared with better-rested volunteers. The study also found that the sleepy volunteers' amygdala communicated less with the part of the brain that determines appropriate emotional responses, suggesting that they weren't doing a good job of tempering their emotions.

When we're sleep deprived, we may also feel glum because tired brains store negative memories more effectively than positive or neutral ones. As a result of all this, Shives says, "If you are chronically sleep deprived, you could act like someone with depression."

5. YOU'VE BECOME A KLUTZ

One moment you're brewing a cup of afternoon tea and the next thing you know, you've spilled it all over your new dress. Researchers have accumulated ample evidence that the sleep deprived have slower and less precise motor skills, but exactly why isn't yet known, says Clete Kushida, MD, PhD, director of Stanford University Center for Human Sleep Research. Sleepy people may be clumsier for several reasons: Impaired reflexes and a lack of focus may make it hard for them to react quickly enough to things that spring up in their path. Another possibility: Sleepiness throws off balance or depth perception. In any case, it's not uncommon for very sleepy people to black out momentarily when the body's urge to sleep gets too strong. So it's possible that your klutziness stems from "microsleeps" that last for a second or two, Kushida says — just long enough to trip on the curb or drop a glass.

Run down? Your exhaustion could be more serious.


YOUR HIGH-ENERGY RECOVERY PLAN

To erase your sleep debt (it may take several weeks), aim for 7 to 8 hours of sleep every night. Meanwhile, here's how to suppress daytime fogginess, stay alert, and get deeper Zzzs.

In the Morning: Soak Up the Sun

Morning rays boost energy by suppressing the sleepiness-inducing hormone melatonin. An early morning walk will help sync your internal clock to the sun, averting an energy slump in the afternoon.

Early Evening: Re-energize With Exercise

Even though you're tired, forcing yourself to do aerobic exercise will energize you for a couple of hours and make it easier to fall asleep at night. Your body temperature naturally falls at night, shortly before bedtime, so the natural dip in temperature that happens about 2 hours after a workout can help you get to bed at a decent hour and wake up refreshed the next morning.

After Lunch: Time Your Nap

Research shows that naps, especially "power naps" of 20 to 30 minutes, help ward off fatigue. To maximize the benefits, try to take a siesta after lunch, when your energy levels are particularly low. Limit rest to less than 30 minutes, or stretch it out to 60 to 90 minutes to avoid grogginess that results from waking up in the middle of deep sleep.

All Day: Work On Something Interesting

Even tired people pay better attention to tasks they find mentally stimulating. So even though you might be tempted to go for the mindless stuff — filing, folding laundry — you'll be more alert if you pick a project that intrigues you.

Eat For Stamina

Big meals and high-sugar foods can cause blood sugar to spike, then plummet, so every few hours while you're recovering, eat a snack (about 100 calories), or try smaller meals (of no more than 400 calories) that contain complex carbohydrates, some protein, and a small amount of healthy fat. Try a handful of nuts or reduced-fat cheese and crackers at low-energy times of the day — typically, early morning and late afternoon.


As Needed: Boost Your Caffeine

Sugary "energy drinks" can be hidden calorie traps, but researchers think there is something about the combination of sugar and caffeine that makes people more alert than caffeine alone does. Next time you are feeling particularly brain-dead, add a tablespoon of honey to your tea or stir a spoonful of sugar into your espresso. And to keep yourself from reaching that state to begin with, try divvying up your one big mug of coffee in the morning into several coffee breaks throughout the day.

More Links:
8 Ways Sleep Deprivation Hurts Your Health
10 Tricks to Reboot Your Sleepy Brain
10 Reasons You Can't Sleep (and What to Do About It)
New Secrets for All-Day Energy

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