What Is Fatigue?
Fatigue is a lingering tiredness that is constant and limiting. With fatigue, you have unexplained, persistent, and relapsing exhaustion. It's similar to how you feel when you have the flu or have missed a lot of sleep. If you have chronic fatigue, or systemic exertion intolerance disease, you may wake up in the morning feeling as though you've not slept. Or you may be unable to function at work or be productive at home. You may be too exhausted to even manage your daily affairs.
In most cases, there's a reason for the fatigue. It might be allergic rhinitis, anemia, depression, fibromyalgia, chronic kidney disease, liver disease, lung disease (chronic obstructive pulmonary disease [COPD]), a bacterial or viral infection, or some other health condition. If that's the case, then the long-term outlook is good.
You can think of fatigue itself as a symptom, but here are some more detailed terms to describe what it might feel like.
- Lack of energy. This is a kind of mental or physical exhaustion that makes it harder to move through daily life. It can impact your ability to work, spend time with your friends or family, or do other activities.
- Drowsiness. You may feel like you have to fight to stay awake, but your tiredness may still be there after you sleep.
- Difficulty thinking. Also called brain fog, you may have trouble paying attention, remembering things, or focusing on detail-oriented tasks.
- Apathy. This refers to a feeling where you lose interest or motivation to do things.
Fatigue vs. lethargy
Doctors don't use the term lethargy very much anymore, but it refers to a drop in consciousness or other brain function. Some causes of lethargy can be serious, including head injuries, brain bleeds, or blood sugar problems.
Tell your doctor if you have unexplained tiredness or trouble thinking clearly. Symptoms of general tiredness, lethargy, and fatigue can overlap. But you may not be able to tell the difference on your own.
Types of Fatigue
Your doctor may put your fatigue in one of three categories:
- Physiologic fatigue can happen from too much exercise, sleep problems, dietary choices, or other nonmedical issues. It usually gets better when you address the lifestyle factor that's causing it.
- Secondary fatigue usually lasts between 1 and 6 months and happens because you have an underlying health condition. Your energy will usually come back over time or with medical treatment.
- Chronic fatigue lasts longer than 6 months and doesn't get better with rest or sleep. It may be caused by a new illness or medical condition.
Types of fatigue may also include:
Sudden tiredness. Your fatigue may come out of nowhere. Some people say it's like "hitting a wall." It can happen with too much physical activity (like running a marathon), infections, or chronic illnesses like multiple sclerosis.
Muscle fatigue. Your body may feel extra heavy, like you're moving through mud or you have to use twice as much effort to do normal things. Strenuous exercise is a common cause of muscle fatigue, but it can also happen with health conditions, including cancer or stroke.
Extreme fatigue after eating. Everyone feels a little sleepy after a meal sometimes, especially if you eat a lot of carbs and protein at once. But tell your doctor if it happens a lot. Medical conditions like celiac disease, diabetes, anemia, or food allergies might be to blame.
COVID fatigue. You can get tired or have less energy for a few weeks after you get sick. During your recovery, you may need to sleep more and take breaks a lot. For some, this lack of energy may linger for longer. Around one in four people get post-acute syndrome of COVID-19 (also known as long COVID), and fatigue is one of the most common symptoms.
Fatigue and pregnancy. This is most common during the first trimester (12 weeks), but it may happen at any point during pregnancy. It may stem from hormonal changes, extra weight, sleep troubles, low iron levels, or raised breathing and heart rate. (You have to pump more blood during pregnancy.)
The following are other common causes of fatigue and how they are resolved.
Allergies, Hay Fever, and Fatigue
Allergic rhinitis is a common cause of chronic fatigue. But allergic rhinitis often can be easily treated and self-managed. To make a diagnosis, your doctor will assess your symptoms. The doctor will also find out, through a detailed history or testing, whether your allergies are triggered by pollens, insects (dust mites or cockroaches), animal dander, molds and mildew, weather changes, or something else.
One way to reduce symptoms of allergic rhinitis—including fatigue—is to take steps to avoid the offending allergen. In addition, proper medication can help with symptoms. Drugs that might help include:
Allergy shots may help in severe cases. This treatment involves weekly shots of increasingly higher solutions of the offending allergens. Allergy shots take time to be effective and are usually given for 3-5 years.
Anemia and Fatigue
Symptoms: Fatigue, dizziness, feeling cold, crankiness
Anemia is the most common blood condition in the U.S. It affects more than 5.6% of Americans. For women in their childbearing years, anemia is a common cause of fatigue. This is especially true for people who have heavy menstrual cycles, uterine fibroid tumors, or uterine polyps.
Anemia is a condition in which you don't have enough red blood cells. It can happen for many reasons. For instance, it may be the result of hemorrhoids or gastrointestinal (GI) problems such as ulcers or cancer. Nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen or aspirin can also lead to GI problems and bleeding. Other causes of anemia include a lack of iron, folic acid, or vitamin B12. Chronic diseases such as diabetes or kidney disease can also cause anemia.
To confirm a diagnosis of anemia, your doctor will give you a blood test. If iron deficiency is the cause of your fatigue, treatment may include iron supplements. You can also add iron-rich foods such as spinach, broccoli, and red meat to your diet to help relieve symptoms. Getting more vitamin C with meals or with iron supplements can help you better absorb the iron and improve your symptoms.
Depression, Anxiety, and Fatigue
Symptoms: Sadness; feeling hopeless, worthless, and helpless; fatigue
Postpartum depression can happen after the birth of a baby. Some people get seasonal affective disorder in the winter, with feelings of fatigue and sadness. Major depression is also one part of bipolar disorder.
With depression, you might be in a depressed mood most of the day. You may have little interest in normal activities. Along with feelings of fatigue, you may eat too much or too little, sleep too much or too little, feel hopeless and worthless, and have other serious symptoms.
Anxiety symptoms may include:
If you are depressed or have regular symptoms of anxiety, talk to your doctor and get a physical exam. If there is no physical cause for the depression or anxiety, your doctor may talk with you about treatment options and may refer you to a psychiatrist or psychologist for a psychological evaluation.
Viral or Bacterial Infection and Fatigue
Symptoms: Fatigue, fever, head or body aches
Fatigue can be a symptom of infections ranging from the flu to HIV. If you have an infection, you'll probably have other symptoms like fever, head or body aches, shortness of breath, or loss of appetite. (They'll vary depending on what infection you have.)
Infections that may cause fatigue include:
Treating the infection often relieves your fatigue. But some infections, including mononucleosis and COVID-19, can lead to long-lasting tiredness.
Fibromyalgia and Fatigue
Fibromyalgia is one of the more common causes of chronic fatigue and musculoskeletal pain, especially in women. Fibromyalgia and chronic fatigue syndrome are considered separate but related disorders. They share a common symptom: severe fatigue that greatly interferes with people's lives.
With fibromyalgia, you may feel that no matter how long you sleep, it's never restful. And you may feel as if you are always fatigued during daytime hours. Your sleep may be interrupted by frequent waking. Yet you may not remember any sleep disruptions the next day. Some people with fibromyalgia live in a constant "fibro fog" -- a hazy feeling that makes it hard to concentrate.
Constant daytime fatigue with fibromyalgia often results in people not getting enough exercise. That causes a decline in physical fitness. It can also lead to mood-related problems. The best way to offset these effects is to try to exercise more. Exercise has tremendous benefits for sleep, mood, and fatigue.
If you do try swimming (or any moderate exercise) to ease fatigue, start slowly. As you become accustomed to the added physical activity, you can raise your time in the pool or gym. Set up a regular time for exercise. Avoid overdoing it, which could add to your fatigue.
Food Allergies, Food Intolerance, and Fatigue
Symptoms: Fatigue, sleepiness, continued exhaustion
Although food is supposed to give you energy, medical research suggests that hidden food intolerances or food allergies can do the opposite. In fact, fatigue may be an early warning sign of food intolerance or food allergy. Celiac disease, which happens when you can't digest gluten, may also cause fatigue.
Ask your doctor about the elimination diet. This is a diet in which you stop eating certain foods linked to a variety of symptoms, including sleepiness within 10-30 minutes of eating them, for a certain period to see if that makes a difference. You can also talk to your doctor about a food allergy test, or invest in a home test such as ALCAT, which may help you identify the offending foods.
Heart Disease and Fatigue
Symptoms: Fatigue from an activity that should be easy
If you're exhausted after an activity that used to be easy -- for example, walking up the steps -- it may be time to talk to your doctor about the possibility of heart disease. Heart disease is the leading cause of death in women. If your fatigue is related to your heart, medication or treatments can usually help correct the problem, cut the fatigue, and restore your energy.
Rheumatoid Arthritis and Fatigue
Symptoms: Fatigue, morning stiffness, joint pain, inflamed joints
Rheumatoid arthritis (RA), a type of inflammatory arthritis, is another cause of excessive fatigue. Because joint damage can result in disability, early and aggressive treatment is the best approach for RA.
Medications that may be used early in mild RA include:
- Nonsteroidal anti-inflammatory drugs
- Disease-modifying antirheumatic drugs
Other drugs used in more serious forms of RA include the anti-cytokine therapies (anti-tumor necrosis factor alpha agents), as well as shots and other forms of treatment.
Other autoimmune disorders, such as lupus and Sjogren's disease, may also cause fatigue.
Sleep Disorders and Fatigue
Symptoms: Chronic fatigue, feeling exhausted upon awakening, snoring
Sleep disorders are a group of conditions that disrupt or prevent restful, restorative sleep. That can take a toll on your health and quality of life, so it's important to look out for signs and symptoms.
Sleep apnea is one of the most common sleep disorders. If you or your partner notices loud snoring and you wake up tired and stay that way, you could have sleep apnea. More than one-third of adults in the U.S. snore at least a few nights a week. But if the snoring stops your breathing for seconds at a time, it could be sleep apnea. Learn more about the best sleep positions and see if sleeping on your stomach is bad or not.
Obstructive sleep apnea causes low blood oxygen levels. That's because blockages prevent air from getting to the lungs. The low oxygen levels also affect how well your heart and brain work. Sometimes, the only clue that you might have sleep apnea is chronic fatigue.
Your doctor may prescribe a medical device called CPAP that helps keep your airways open while you sleep. In severe cases of sleep apnea, surgery may help. The surgeon will remove tissues that are blocking the airways. If left untreated, sleep apnea can raise your risk of a stroke or heart attack.
But sleep apnea is just one of many sleep disorders that cause fatigue. Other common types include:
- Insomnia: You can't get to sleep or stay asleep through the night.
- Narcolepsy: You feel extremely sleepy during the day and may fall asleep suddenly.
- Restless legs syndrome: Your legs feel uncomfortable and you have an urge to move them as you fall asleep.
- REM sleep behavior disorder: You act out dreams in your sleep with talking, walking, or swinging your arms.
Talk with your doctor about a sleep study (polysomnogram) to find out if you have a sleep disorder. Lose weight if you are overweight, and if you smoke, stop. Both obesity and smoking are risk factors for sleep apnea. Sleeping on your side instead of your back may help stop mild sleep apnea.
Diabetes and Fatigue
Symptoms: Extreme fatigue, raised thirst and hunger, more urination, unusual weight loss
The incidence of type 2 diabetes is rising in children and adults in the U.S. If you have symptoms of type 2 diabetes, call your doctor and ask to be tested. While finding out you have diabetes may be frightening, type 2 diabetes can be self-managed with guidance from your doctor.
Treatment for type 2 diabetes may include:
- Losing excess weight
- Increasing physical activity
- Maintaining strict blood glucose control
- Taking diabetes medications (insulin or other drugs)
- Eating a low-glycemic index carbohydrate diet or, though controversial, a low-carbohydrate diet
Underactive Thyroid (Hypothyroidism) and Fatigue
Symptoms: Extreme fatigue, sluggishness, feeling run-down, depression, cold intolerance, weight gain
The problem may be a slow or underactive thyroid. This is known as hypothyroidism. The thyroid is a small, butterfly-shaped gland that sits at the base of your neck. It helps set the rate of metabolism, which is the rate at which the body uses energy.
According to the American Thyroid Foundation, about 17% of all women will have a thyroid disorder by age 60. And most won't know it. The most common cause is an autoimmune disorder known as Hashimoto's thyroiditis. Hashimoto's stops the gland from making enough thyroid hormones for the body to work the way it should. The result is hypothyroidism or a slow metabolism.
Blood tests known as T3 and T4 will detect thyroid hormones. If these hormones are low, synthetic hormones (medication) can help you return to normal levels, and you should begin to feel better fairly rapidly.
If you have been diagnosed with cancer, fatigue is often part of the disease itself or a side effect of some treatments. Cancer-related fatigue is far more severe than feeling tired if you don't have cancer. You might feel too tired to move around, and you may also feel weak. It can happen with the more common types of cancer, such as lung cancer, colon cancer, or breast cancer; with the rarer types, such as cancers of the brain and spinal cord; and with blood cancers, including leukemia, lymphoma, and multiple myeloma.
If you haven't been diagnosed with cancer, feeling very tired can be a symptom, but there are many other more likely causes. If you have other symptoms or if your fatigue doesn't ease after you get more rest and make other lifestyle changes, see your doctor and tell them how you're feeling.
What Causes Your Fatigue?
Many physical and mental illnesses, as well as lifestyle factors, can cause your fatigue and that can make it hard to diagnose. In some cases, it might be something simple and easy to fix, like avoiding caffeine at bedtime. But other causes, like heart disease or COPD, are serious, and you may need to start long-term treatment right away.
Your doctor can help you sift through your health issues, as well as your diet, exercise, and other lifestyle habits, to zero in on the cause and help you on the road to recovery.
Work with your doctor to find the underlying cause of your fatigue. You may need lifestyle changes or medical treatment to manage your symptoms.
When it comes to general fatigue treatment, here are some things that might help:
Find the right amount of movement. You may have more energy if you exercise regularly. A good goal to aim for is at least 30 minutes of physical activity most days of the week. But take care not to overdo it. Too much exercise saps your energy, too.
Follow a nutritious eating plan. There isn't one food that'll wipe out your fatigue, but you may feel less tired if you follow a plant-forward anti-inflammatory diet high in fiber and antioxidants. Try to eat more fruits, vegetables, whole grains, and fatty fish while avoiding ultra-processed snacks high in added sugar. Opt for small meals more often if you get tired after big ones.
Maintain a healthy weight. There isn't a perfect body size that works for everyone. But if you have a bigger body, you might feel less fatigued if you lower your weight. Talk to your doctor about treatment options if you're having trouble maintaining a size that feels good for you.
Get good sleep. Everyone's sleep needs are different, but most adults need 7-9 hours of quality shuteye every night. Anything less than that is likely to leave you feeling fatigued the next day.
Here are some steps you can take to get better sleep:
- Try to go to bed and get up at the same time every day
- Don't take daytime naps
- Skip afternoon caffeine
- Limit or avoid alcohol, especially close to bedtime
If healthy habits don't help you fall asleep or stay asleep, talk to your doctor. There are treatments for insomnia.
Find time to relax. Ongoing stress can make it hard to sleep or may boost chemicals in your body that leave you feeling worn out. In addition to exercising, eating a healthy diet, and getting good sleep, healthy ways to manage stress include:
- Taking breaks throughout the day
- Meditation or mindfulness
- Yoga or tai chi
- Hanging out with your friends
- Connecting with your community or faith groups
A mental health professional like a psychologist, social worker, or counselor can also be a good resource.
Seek help for substance use disorder. Fatigue is a common problem for people who misuse alcohol or other substances, including drugs like cocaine, marijuana, or opioids.
Get medical treatment. See your doctor if lifestyle changes don't boost your energy. They'll help you figure out if you have a health condition that needs treatment or if fatigue is a side effect of one of the medications you're taking.
Along with medical treatment for any hidden health problems, your doctor may suggest:
- Exercise therapy
- Cognitive behavior therapy
- Stimulant drugs
Anti-fatigue lenses. These are special lenses that may lessen eye strain if you read a lot or look at a computer screen for long periods. These glasses may ease eye tiredness but probably won't reduce overall fatigue. Ask your eye doctor about them the next time you get your vision checked.
Fatigue can be caused by a range of medical conditions. If you're consistently waking up tired or having trouble staying alert during the day, talk with your doctor about your symptoms. They can help you figure out if your fatigue is a symptom of another condition and try to find the treatment that's right for you.
Here are some answers to frequently asked questions about fatigue.
What is the main cause of fatigue?
Usually, lifestyle factors are the cause. For example, fatigue may stem from lack of sleep, dietary choices, and too much or too little exercise. Other common causes of fatigue include medication side effects, depression, allergies, viral infections, pregnancy, or medical conditions.
What is the difference between being tired and being fatigued?
People use these terms interchangeably, but tiredness usually refers to short-term lack of energy that gets better with rest or sleep. Fatigue, on the other hand, is more of a constant mental or physical exhaustion that impacts your work, social life, or ability to do everyday things. Often, fatigue doesn't get better with sleep.