The truth about what's causing your mid-day fatigue, plus expert advice on how to beat your exahustion

By Chris Artis

You know the signs of fatigue. It seems like lead weights are tied to your limbs; you can't focus at work; all you want to do is put your head down, right here, and close your eyes-you're exhausted! If you just took a redeye flight across country or your toddler kept you up half the night or you're getting over the flu, at least you know why you're feeling this way. But what if you've been clocking a full eight hours of slumber each night and still feel exhausted every day? Here are six surprising reasons you're feeling sluggish, along with expert advice on beating the bushed blues.

You May Have Chronic Fatigue Syndrome



It's an enigmatic disease, often misdiagnosed. And while there have been high profile cases-bestselling author Laura Hillenbrand documented her fight against CFS in a National Magazine Award-winning New Yorker piece-some in the medical community still doubt its very existence. But new research, such as a discovery made during a recent Stanford study on CFS , may help doctors diagnose the disease more easily. Jacob Teitelbaum, MD, sleep expert and author of The Fatigue and Fibromyalgia Solution, says, "with more and more studies proving conclusively that CFS is a real illness, physicians are starting to make the shift to understanding and compassion." If diagnosed, Dr. Teitelbaum recommends seeing a physician who specializes in sleep disorders and offers an integrated approach to treatment. (Find out what you need to know about chronic fatigue syndrome.)

You're Not Exercising Enough



As if there weren't enough reasons already to motivate you to drag your butt off that couch, add recurring fatigue to the list. Exercise improves circulation and distributes more oxygen throughout body tissue, and The National Sleep Foundation cites studies that suggest that "exercise significantly improves the sleep of people with chronic insomnia."

You Exercise Too Much



Exercise relieves stress and that helps you sleep. But you can have too much of a good thing. Carolyn Dean, MD, ND, author of Magnesium: The Missing Link To Better Health explains that heavy exercise can result in the depletion of key minerals including magnesium, which is particularly important to maintaining energy. "Magnesium is known as an energy mineral and an anti-stress mineral and is required for the body to produce and store energy." If you've sweated heavily, you've sweated out magnesium, so make sure you replenish it. Dr. Dean says that one of the most absorbable forms is a powdered magnesium citrate which can be dissolved in water and sipped throughout the day. Want to feel even more upbeat? Check out these 10 Tips for Everlasting Energy.

You're Eating Dinner Way Too Late



If you eat a late dinner, particularly a large and rich one as many Americans do, you dramatically increase your risk of developing acid reflux disease, according to Jamie Koufman, MD and author of The Chronic Cough Enigma. Acid reflux and the use of (costly) medications to treat it are associated with an increased risk of developing esophageal cancer-reason enough to avoid getting it! It can also seriously disturb your sleep and make you tired during the day. Dr. Koufman suggests eating a moderately sized dinner, and finish at least three to four hours before bed time. After dinner, don't immediately flop on the couch. Stay upright or take a walk. Lying down right after eating makes reflux much more likely.

You Have Sleep Apnea



Sleep apnea occurs when the muscles in the back of your throat relax, shrinking the airway and causing a cessation of breathing for ten seconds or longer. This can happen as often as 30 times an hour, all night, preventing you from reaching a restful stage of sleep. It can also cause a drop in the oxygen saturation of the blood. If that sounds exhausting, it is. And according to Rich Hirschinger, DDS, MBA and lecturer at UCLA Orofacial Pain and Dental Sleep Medicine, one in five American women are afflicted. But it can be treated. "A CPAP (continuous positive airway pressure) machine is the gold standard treatment," says Dr. Hirschinger. "And a properly trained dentist can make a MAD (mandibular advancement device). These devices bring the jaw forward during sleep, which pulls the tongue off the back of the throat and opens the airway."

You're Dehydrated



So many things we do can make us dehydrated. If you regularly take that hard spinning class, have a couple glasses of wine with dinner (alcohol is a diuretic), fuel with coffee all day (caffeine is a stimulant and a diuretic!), and you aren't drinking enough water, you may be spending a lot of time in a state of mild dehydration. Louis Morledge, MD, a physician and Clinical Professor at New York Medical College, says that mild dehydration leads to reduced levels of sodium and potassium, as well as lower blood pressure and hypertension-all of which cause fatigue. There is no one correct amount of water you should drink per day. It really depends on your lifestyle. But be mindful of your H2O intake and pay attention to the color of your pee, too. If it's amber or orange, you're not drinking enough water. Still tired? Now, get to bed with the help of our 13 Expert-Approved Sleep Tips.