Fatigue is when a person feels a strong need to rest and has so little energy that starting and sustaining activity is difficult.
Fatigue is normal after physical exertion, prolonged stress, and sleep deprivation. However, fatigue that increases and develops after activities that previously did not cause fatigue may be a symptom of a disease.
Fatigue can be classified into 3 categories
Recent fatigue is fatigue that lasts less than 1 month.
Prolonged fatigue is fatigue that lasts from 1 to 6 months.
Chronic fatigue is fatigue that lasts longer than 6 months.
It is important to distinguish fatigue from weakness of the muscles, difficulty breathing, and sleepiness. Extensive conversations with a doctor may be needed to clarify the difference.
Causes of Fatigue
Most serious and many minor illnesses cause fatigue. However, most of these disorders have other more prominent symptoms (for example, pain, cough, fever, or jaundice [yellowing of the skin]) that are likely to bring the person to the doctor. This discussion focuses on disorders in which fatigue is the first or most severe symptom.
Common causes
There is no firm dividing line between causes based on duration of fatigue, but doctors find that certain causes tend to be related to how long people have had fatigue before they seek medical care.
Recent fatigue (lasting less than 1 month) has many causes, but the most common are the following:
Anemia (low red blood cell count)
Stress and/or depression
For prolonged fatigue (lasting 1 to 6 months), the most common causes are the following:
An underactive thyroid gland (hypothyroidism)
Sleep disturbances (such as sleep apnea)
For chronic fatigue (lasting longer than 6 months), the most common causes are the following:
Chronic fatigue syndrome (now sometimes called myalgic encephalomyelitis or systemic exertion intolerance disease)
Postviral fatigue syndrome
Mental health condition (such as depression)
Chronic fatigue syndrome, also known as myalgic encephalomyelitis or systemic exertion intolerance disease, is a disease of unknown cause that results in fatigue and certain other symptoms. Not everyone who has fatigue for no apparent reason has chronic fatigue syndrome. People with COVID-19 may have fatigue and other symptoms that last for weeks or even months, which is known as "long COVID" or "long-haul COVID" and resembles chronic fatigue syndrome.
Less common causes
Stopping cocaine and methamphetamines can cause severe fatigue. Less common causes of prolonged or chronic fatigue include adrenal gland underactivity and pituitary gland underactivity.
Evaluation of Fatigue
People vary in what they consider to be fatigue and how they describe it. There are also few ways for a doctor to positively confirm fatigue or tell how severe it is. Doctors usually start an evaluation by trying to distinguish true fatigue from other symptoms that people may refer to as fatigue.
Weakness: Weakness is lack of muscle strength that makes it difficult for people to move the affected muscles. Weakness is typically a symptom of a nervous system or muscle disorder. Disorders such as myasthenia gravis and Eaton-Lambert syndrome can cause weakness that worsens with activity, which may be confused with fatigue.
Shortness of breath: People, such as those with certain heart and lung disorders, become short of breath with activity but do not feel fatigued at rest.
Drowsiness: Excessive sleepiness is a symptom of sleep deprivation (for example, caused by lifestyle or by disorders such as allergic rhinitis, gastroesophageal reflux, painful musculoskeletal disorders, sleep apnea, and severe long-lasting disorders). Yawning and lapsing into sleep during daytime hours are common. However, many people with fatigue have disturbed sleep, so symptoms of sleep deprivation and fatigue can overlap.
Warning signs
In people with fatigue, certain symptoms and characteristics are cause for concern. They include
Persistent, unintentional weight loss
Chronic fever or night sweats
Swollen lymph nodes throughout the body
Muscle weakness and/or pain
Serious accompanying symptoms (for example, coughing up or vomiting blood, bloody or black stools, shortness of breath, swelling in the abdomen, confusion, or suicidal thoughts)
Involvement of more than one organ system (for example, rash plus joint pain and stiffness)
Headache or loss of vision, particularly with muscle pains, in an older adult
When to see a doctor
All people feel fatigue occasionally, and not every case of fatigue requires evaluation by a doctor, particularly those that accompany an acute (sudden) illness (such as an acute infection) or that go away after a week or two. However, fatigue that lasts longer or has no obvious explanation should be evaluated.
Older adults with fatigue and a new or unusual headache or loss of vision, and people who have other serious symptoms with fatigue, should see a doctor immediately. Even if they have no other symptoms, older adults with fatigue should see their doctor as soon as possible. Other people who have other warning signs should see a doctor in a few days. People who have no additional warning signs other than fatigue should call their doctor. The doctor can help decide how quickly they need to be seen. Typically a delay of a week or so is not harmful.
What the doctor does
Doctors first ask questions about the person's symptoms and medical history. Doctors then do a physical examination. What they find during the history and physical examination often suggests a cause of the fatigue and the tests that may need to be done (see table Some Common Causes and Features of Prolonged or Chronic Fatigue).
Doctors ask the person
To describe what is meant by fatigue as precisely as possible
How long fatigue has lasted
When fatigue occurs in relation to rest and activity
What other symptoms occur (such as fever, night sweats, or shortness of breath)
What measures relieve or worsen fatigue
How fatigue affects the person's work and social activities
Women are asked about their menstrual history. All people are asked about diet, anxiety, depression, and alcohol and drug use (including use of over-the-counter medications and illicit drugs).
Doctors then do a physical examination. Because many disorders can cause fatigue, the physical examination is very thorough, particularly in people with chronic fatigue. Doctors also do a neurologic examination to evaluate the person's muscle strength and tone, reflexes, gait, mood, and mental status. The history and physical examination are more likely to reveal the cause of fatigue of more recent onset. A cause is also more likely to be found when fatigue is one of many symptoms than when fatigue is the only symptom. Fatigue that worsens with activity and lessens with rest suggests a physical disorder.
Some Common Causes and Features of Prolonged or Chronic Fatigue
Cause | Common Features* | Diagnostic Approach |
|---|---|---|
Blood disorders or cancers | ||
Decreased exercise tolerance and shortness of breath greater than expected during activity Sometimes paleness | CBC | |
Cancers (such as digestive tract cancer, lung cancer, leukemia, lymphoma, multiple myeloma) | Widespread lymph node swelling, weight loss, and/or night sweats With multiple myeloma, low back or other bone pain, often severe at night | CBC Sometimes other tests, such as endoscopy or imaging tests |
Infections | ||
Sometimes jaundice (yellowing of the skin), loss of appetite, and fluid in the abdomen | Blood tests to determine how well the liver is functioning and to identify the hepatitis virus Sometimes liver biopsy | |
Fever Sometimes cough and respiratory symptoms Sometimes loss of taste and smell | Test for SARS-CoV-2 virus | |
Enlarged spleen and lymph nodes, fever, and night sweats | Sometimes blood tests for antibodies to cytomegalovirus | |
Heart valve infection (endocarditis) | Fever and night sweats Sometimes joint pains Usually in people who have heart murmurs or inject drugs intravenously | Cultures of blood samples and echocardiography |
Fever, night sweats, and frequent infections Sometimes difficulty breathing, cough, diarrhea, and/or rash | HIV blood test | |
Recent sore throat and lymph node swelling | Mononucleosis blood test | |
Other infections (for example, fungal pneumonias such as histoplasmosis, parasitic infections, or tuberculosis) | Fever, night sweats, and weight loss Sometimes cough, difficulty breathing, and coughing up blood | Tests based on which type of infection seems likely |
Other disorders and causes | ||
Shortness of breath, difficulty breathing when lying down that is relieved when upright (orthopnea), and/or swelling | Blood tests of kidney function | |
Systemic rheumatic disorder (for example, rheumatoid arthritis or systemic lupus erythematosus [lupus]) | Fever, night sweats, weight loss, joint pain, rash, and/or other organ involvement (for example, effects on the heart or lungs) | Blood tests for abnormal antibodies |
Deconditioning | A history of lack of exercise or being bedbound or hospitalized | Only a doctor's examination |
Diabetes (sometimes, other symptoms often more prominent) | Excessive thirst, excessive urination, increased appetite, and unexplained weight gain or loss | Measurement of sugar (glucose) level in the blood after the person fasts overnight and sometimes glucose tolerance testing |
Drugs: Antidepressants, older antihistamines, antihypertensives, diuretics that cause low potassium levels in the blood, muscle relaxants, illicit drugs, and sedatives | History of taking a medication or drug known to cause fatigue | Only a doctor's examination |
Headache, pain in the jaw when chewing, pain when combing hair, loss of vision, and/or muscle pains in a person over 50 | ESR and/or CRP; temporal artery ultrasound and/or biopsy | |
Mental health conditions: Anxiety, depression, drug dependence, panic disorder, or somatization disorder (physical symptoms caused mainly by anxiety) | Anxiety, sadness, loss of appetite, and unexplained sleep disturbance With somatization disorder, an excessive preoccupation with physical symptoms | Only a doctor's examination |
Fatigue worse with exposure to heat Past symptoms of nervous system malfunction (such as numbness, loss of coordination, and weakness), particularly if people had more than one episode of symptoms | Brain and/or spinal cord MRI | |
Pregnancy | Cessation of menstrual periods, breast tenderness, morning sickness, and abdominal swelling | Pregnancy test |
Excessive daytime sleepiness, frequent awakenings, breathing interruptions during sleep, difficulty falling asleep, unrefreshing sleep | Sleep testing (polysomnography or home testing) | |
Underactive thyroid gland (hypothyroidism) | Inability to tolerate cold, weight gain, constipation, and coarse skin | Blood tests of thyroid function |
Weight loss Sometimes loss of appetite, foul-smelling stool, abdominal pain, or a combination | A doctor's examination Sometimes other tests | |
Disorders of unknown cause | ||
Chronic fatigue syndrome (now sometimes called myalgic encephalomyelitis or systemic exertion intolerance disease) | Sore throat, sleep that is not refreshing, difficulty with concentration or short-term memory, muscle aches, joint pain, headaches, and/or tender lymph nodes in the neck or under the arms | A doctor's examination |
Longstanding and widespread muscle and bone pain in areas outside the joints, trigger points, lower abdominal pain, gas, bloating, constipation or diarrhea, migraines, and anxiety | A doctor's examination | |
* Features include symptoms and the results of the doctor's examination. Features mentioned are typical but not always present. | ||
CBC = complete blood count; ESR = erythrocyte sedimentation rate; HIV = human immunodeficiency virus; MRI = magnetic resonance imaging. | ||
Testing
The need for tests depends on what doctors find during the history and physical examination. For example, doctors test for human immunodeficiency virus infection (HIV) and tuberculosis if people have risk factors. Testing for other infections or cancer is usually done only when people's findings suggest these causes. In general, people who have had fatigue for a long time and those who have warning signs are more likely to require testing.
If people do not have any other findings besides fatigue, many doctors do a few common blood tests. For example, they may do a complete blood count, blood tests to measure liver, thyroid gland, and kidney function, and a blood test called the erythrocyte sedimentation rate that suggests the presence of inflammation. However, such blood testing often does not reveal the cause.
Treatment of Fatigue
There are no approved medication treatments for myalgic encephalomyelitis/chronic fatigue syndrome/systemic exertion intolerance disease. Treatment is directed at the cause of the fatigue. People with chronic fatigue syndrome or fatigue with no clear cause may be helped with physical therapy that includes increasing degrees of exercise and with psychological support (for example, cognitive-behavioral therapy). Focusing on improving sleep and improving pain may also be helpful.
Essentials for Older Adults: Fatigue
Although it is normal for people to slow down as they age, persistent or severe fatigue is not normal. Fatigue is often the first symptom of a disorder in older adults. For example, the first symptom of pneumonia in an older adult may be fatigue rather than any pulmonary symptoms (such as cough or difficulty breathing) or fever. The first symptom of other diseases, such as giant cell arteritis, may also be fatigue. Because a serious illness may become apparent soon after sudden fatigue in older people, it is important to determine the cause quickly.
Key Points
Fatigue is a common symptom.
Fatigue is especially concerning if accompanied by certain warning symptoms, such as persistent, unintentional weight loss or chronic fever or night sweats.
If a doctor uncovers no findings suggesting a cause of fatigue, tests are often not helpful in identifying the cause.
Successful treatment of chronic fatigue may take work and persistence.
Fatigue in older adults is not a normal part of aging.
