The Most Common Extreme Fatigue Causes, According to Experts

Maybe it's not just a lack of sleep.

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You got a full eight hours but are still exhausted; what's the deal? Finding out what's causing your fatigue can be challenging.

In fact, getting to the bottom of what's behind a patient's exhaustion is among the hardest questions primary care doctors answer, Cory Fisher, DO, who specializes in family medicine at Cleveland Clinic, tells Health.

Here, you'll find a list of the conditions most often associated with fatigue, plus lifestyle habits that can contribute to the problem.


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Anemia means you don't have enough red blood cells to take oxygen to all the distant outposts of the body. Less oxygen means lower energy and more fatigue, and anemia is among the most common causes of chronic fatigue, Dr. Fisher explains.

The most common form of anemia occurs when you're low in iron, which, in turn, could be the result of gastric bypass surgery, heavy periods, chronic diseases, or vitamin deficiencies.

A simple test can verify if you have anemia. Treatment depends on what's causing your lack of red blood cells.

Any underlying conditions should be addressed first. Otherwise, your doctor may recommend vitamin supplements and changes in your diet.

Celiac Disease

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Celiac is an autoimmune disease that causes the immune system to attack the small intestine when a person eats gluten, a protein found in wheat, rye, and barley.

"The small intestine is so disturbed, you're not necessarily getting the nutrients that you need," says Gerald Bernstein, MD, Endocrinologist and former Coordinator of the Friedman Diabetes Program at Lenox Hill Hospital in New York City.

This can lead not only to fatigue but also anemia, diarrhea, and weight loss.

The only treatment is avoiding foods that contain gluten. Naturally gluten-free foods include fruits and vegetables, fish and meat, beans, rice, potatoes, and quinoa.

Sleep Apnea

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Sleep apnea is more than just trouble getting enough sleep. It's when your airways close and you actually stop breathing repeatedly during the night, which, needless to say, wakes you up pretty quickly. Because of those frequent disruptions, people with sleep apnea walk around exhausted.

It's more common in people who are obese and, like obesity, adds to your risk for high blood pressure, heart disease, and stroke.

The go-to treatment for sleep apnea is a continuous positive airway pressure (CPAP) device, which keeps the airways open while you sleep. CPAP machines work, but many people don't like wearing them and are turning to oral devices now instead.

The only actual cure for sleep apnea is losing weight or surgery to remove tissue from your throat.

Chronic Fatigue Syndrome

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The defining symptom of chronic fatigue syndrome (CFS) is, of course, fatigue–but with specific characteristics. It's fatigue that lasts for at least six months, that gets worse with mental or physical exertion, and that doesn't get better no matter how much you rest. It's more common in women in their forties and fifties.

No one is sure what causes CFS, and it's usually diagnosed by ruling out other conditions and taking into account other common symptoms like a sore throat, swollen lymph nodes, muscle aches, and trouble concentrating.

There's no cure for the condition or even a specific treatment. Instead, lifestyle measures like pacing yourself can give you more energy. Some people benefit from medication or cognitive therapy.


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Fatigue isn't the most pronounced symptom of fibromyalgia—that's pain—but it's a big one, along with poor-quality sleep and memory and mood problems. The condition is more common in women.

Scientists don't completely understand fibromyalgia but believe it may be caused by changes in the way your brain processes pain signals.

While there's no cure, a variety of medications can help control fibromyalgia symptoms. Exercise, relaxation, and stress-reduction measures may help.

Certain antidepressants may help ease fibromyalgia fatigue, and not just by controlling pain, which is exhausting in and of itself, but through other mechanisms as well.

Chronic Pain

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Being in constant pain, for any reason. will tire you out.

"It requires energy," says Dr. Bernstein. Your body is busy coping with the inflammation that's causing the disease. Dealing with pain can also make it hard to sleep and exercise, adding to the run-down feeling. Certain pain-relieving drugs may also sap you of energy."

"Any chronic disease, not just chronic pain, can cause fatigue because it diverts energy away from everyday living," Dr. Bernstein says.

If you suffer from chronic pain and think it might be contributing to your fatigue, speak with your doctor about options for treating the underlying condition causing the pain while also addressing your exhaustion.

Thyroid Problems

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Both an underactive and an overactive thyroid can cause fatigue. The more common culprit though is an underactive gland, which doesn't produce enough thyroid hormone. Having an underactive thyroid, also called hypothyroidism, can also mean weight gain and sore muscles.

"With an underactive thyroid, the body compensates up to a point, but if the gland is unable to put out a normal amount of thyroid hormone, the body will slowly lose the ability to create energy, not only for day-to-day activity, but also for the growth and metabolism of cells," says Dr. Bernstein.

Hypothyroidism is treated with replacement thyroid hormone. Different medications and sometimes surgery can treat an overactive gland, also called hyperthyroidism.


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The stress of everyday life can make you tired. Being depressed or anxious can compound this significantly.

Fatigue due to depression is more than just a lack of energy going about your day; it's also apathy, problems focusing and remembering, and feeling overwhelmed and unmotivated. That can become a vicious cycle, with the depression fueling the fatigue, which fuels the depression.

And some antidepressants may make it worse. If you suffer from depression and fatigue, consider talking to your doctor about antidepressants that don't cause fatigue and alternative treatments like cognitive behavioral therapy.

Multiple Sclerosis

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The fatigue of multiple sclerosis, a chronic disease that damages the nerves, can have several different causes, some of which would exhaust anybody.

Problems with your bladder may get you up several times a night, as might muscle spasms. Depression, common in MS, can add to fatigue, as can all the energy it can take to do once-simple tasks such as brushing your teeth.

Then there's lassitude, a type of fatigue that only people with MS get. This so-called "MS fatigue" is more severe, usually happens every day, gets worse with heat and humidity, and can come out of seemingly nowhere.

Talk to your doctor about treatments for MS and treatment for specific symptoms including fatigue. These can range from physical or occupational therapy to medications to staying out of the heat.

Lifestyle Habits

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Sometimes, chronic exhaustion isn't caused by a separate health condition. It can be caused by a lifestyle habit, which is both good and bad: On the one hand, you don't have to receive treatment for another disorder, but on the other, you'll have to adjust your routine to get better.

"When we'll do a good exam [and] nothing really reveals itself, we're left with talking in-depth about self-care," Dr. Fisher says.

A number of habits can cause you to feel tired. On the more obvious side is how much sleep you're getting each night, but there's much, much more to it than that.

For starters, your exercise habits can affect how much energy you have, as can your diet and how much screen time you get. If you think a specific part of your routine is the culprit, consider asking your primary care physician how you can adjust to start feeling less tired.

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