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 it may be one of the symptoms, or, occasionally, the first symptom of a disorder.
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) 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.
There is no firm dividing line between causes based on duration of fatigue. However, doctors find that certain causes tend to be more common depending on 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:
For prolonged fatigue (lasting 1 to 6 months), the most common causes are the following:
For chronic fatigue (lasting longer than 6 months), the most common causes are the following:
Chronic fatigue syndrome Chronic Fatigue Syndrome Chronic fatigue syndrome, also called myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), refers to long-standing severe and disabling fatigue without a proven physical or psychologic... read more (now sometimes called myalgic encephalomyelitis or systemic exertion intolerance)
Postviral fatigue syndrome
Chronic fatigue syndrome is a disorder 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 COVID-19 COVID-19 is an acute respiratory illness that can be severe and is caused by the coronavirus named SARS-CoV-2. Symptoms of COVID-19 vary significantly. Two types of tests can be used to diagnose... read more may have 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 can cause severe fatigue. Less common causes of prolonged or chronic fatigue include adrenal gland underactivity and pituitary gland underactivity.
Evaluation of Fatigue
Fatigue can be highly subjective. People vary in what they consider to be fatigue and how they describe it. There are also few ways to objectively 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 Weakness refers to loss of muscle strength. That is, people cannot move a muscle normally despite trying as hard as they can. However, the term is often misused. Many people with normal muscle... read more : 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 Myasthenia Gravis Myasthenia gravis is an autoimmune disorder that impairs communication between nerves and muscles, resulting in episodes of muscle weakness. Myasthenia gravis results from malfunction of the... read more and Eaton-Lambert syndrome Eaton-Lambert Syndrome Eaton-Lambert syndrome is an autoimmune disorder that impairs communication between nerves and muscles, causing weakness. Eaton-Lambert syndrome usually precedes, occurs with, or develops after... read more can cause weakness that worsens with activity, which may be confused with fatigue.
Shortness of breath Shortness of Breath Shortness of breath—what doctors call dyspnea—is the unpleasant sensation of having difficulty breathing. People experience and describe shortness of breath differently depending on the cause... read more : 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 Insomnia and Excessive Daytime Sleepiness (EDS) The most commonly reported sleep-related problems are insomnia and excessive daytime sleepiness. Insomnia is difficulty falling asleep or staying asleep, waking up early, or a disturbance in... read more 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.
In people with fatigue, certain symptoms and characteristics are cause for concern. They include
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 illness (such as an acute infection) or that go away after a week or so. However, fatigue that seems to last longer or has no obvious explanation should be evaluated.
Older adults with a new or different headache or loss of vision and people who have serious accompanying symptoms 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 warning signs should call their doctor. The doctor can 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 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 Overview of Over-the-Counter Drugs Over-the-counter (OTC) drugs are those available without a prescription. OTC drugs enable people to relieve many annoying symptoms and to cure some diseases simply and without the cost of seeing... read more and recreational drugs Recreational Drugs and Intoxicants ).
Doctors then do a physical examination. Because many disorders can cause fatigue, the physical examination is very thorough, particularly in people with chronic fatigue. In particular, 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.
The need for tests depends on what doctors find during the history and physical examination. For example, doctors test for human immunodeficiency virus infection Human Immunodeficiency Virus (HIV) Infection (HIV) and tuberculosis Tuberculosis (TB) Tuberculosis is a chronic contagious infection caused by the airborne bacteria Mycobacterium tuberculosis. It usually affects the lungs, but almost any organ can be involved. Tuberculosis... read more 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
Treatment is directed at the cause of the fatigue. People with chronic fatigue syndrome Chronic Fatigue Syndrome Chronic fatigue syndrome, also called myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), refers to long-standing severe and disabling fatigue without a proven physical or psychologic... read more or fatigue with no clear cause may be helped with physical therapy that includes increasing degrees of exercise and with psychologic support (for example, cognitive-behavioral therapy). Focusing on improving sleep and improving pain may also be helpful.
Essentials for Older People: Fatigue
Although it is normal for people to slow down as they age, fatigue is not normal. Fatigue is more often the first symptom of a disorder in older people. For example, the first symptom of pneumonia Overview of Pneumonia Pneumonia is an infection of the small air sacs of the lungs (alveoli) and the tissues around them. Pneumonia is one of the most common causes of death worldwide. Often, pneumonia is the final... read more in an older woman may be fatigue rather than any pulmonary symptoms (such as cough or difficulty breathing) or fever. In older people, the first symptom of other disorders, such as giant cell arteritis Giant Cell Arteritis Giant cell arteritis is chronic inflammation of large and medium arteries of the head, neck, and upper body. Typically affected are the temporal arteries, which run through the temples and provide... read more , may also be fatigue. Because serious illness may become apparent soon after sudden fatigue in older people, it is important to determine the cause as quickly as possible.
Key Points about Fatigue
Fatigue is a common symptom.
Fatigue caused primarily by a physical disorder increases with activity and lessens with rest.
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 people is not a normal part of aging.