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What causes fatigue? 251 possible conditions

What Is Fatigue?

Fatigue is a term used to to describe the general overall feeling of tiredness and/or a lack of energy. Other words that are sometimes used in place of fatigue include exhaustion, weariness, and lethargy. According to the National Institutes of Health, feeling fatigued is not the same different from just feeling drowsy or sleepy. (NIH) When you are fatigued, you have no motivation and no energy. Being sleepy may be a symptom of fatigue, but it is not the same thing.

The organization also states that fatigue is a very common symptom for a number of medical conditions—both serious and non-serious—and also a natural result of some lifestyle choices.

If your fatigue has no apparent cause, and it not going away with proper rest and nutrition, you should see your doctor. He or she can help to diagnose what is causing your fatigue and work with you to treat it.

Possible Explanations for Fatigue

There are many potential causes of fatigue, which can be divided into three general categories—lifestyle factors, medical issues, and mental health issues.

Lifestyle Factors

If you are experiencing fatigue, your activities and other lifestyle choices may be the root cause. In these cases, the reasons behind your feelings of exhaustion are often fairly easy to pinpoint. Fatigue can be caused by:

  • physical activity and excessive physical exertion
  • lack of activity
  • lack of sleep
  • being bored
  • being overweight or obese
  • periods of emotional stress
  • grief
  • taking certain medications, such as antidepressants or those that have a sedative effect
  • using alcohol on a regular basis
  • using street drugs, such as cocaine, on a regular basis
  • using narcotics
  • consuming caffeine
  • not eating a proper and nutritious diet

Medical Issues

Some medical issues and conditions that can lead to fatigue are:

  • anemia
  • pain
  • Addison’s disease (a disorder affecting your hormone levels)
  • hypothyroidism (underactive thyroid)
  • hyperthyroidism (overactive thyroid)
  • arthritis
  • insomnia and other sleeping disorders
  • eating disorders, such as anorexia
  • autoimmune disorders
  • fibromyalgia
  • congestive heart failure
  • cancer
  • diabetes
  • kidney or liver disease
  • infection
  • chronic fatigue syndrome
  • chronic obstructive pulmonary disease (or COPD, which makes it difficult to breathe)
  • emphysema
  • restless legs syndrome

Mental Health Issues

Those who struggle with anxiety and depression may experience fatigue as a symptom of their condition.

When Is it Time to See Your Doctor and How Will Your Physician Likely Address Your Fatigue?

You should arrange a visit to your doctor if you are fatigued and:

  • you cannot think of anything that might account for your feelings of weakness or fatigue
  • you have unexplained fatigue, along with a higher-than-normal body temperature
  • you have unexplained fatigue and unexplained weight loss
  • you regularly have trouble sleeping through the night or have insomnia
  • you are constipated
  • you believe you may be depressed
  • you are very sensitive to colder temperatures

The Mayo Clinic recommends seeking medical help if you have been experiencing fatigue for two weeks or more and you have made efforts to address the most common lifestyle causes, such as lack of rest, stress, and poor eating habits, without success. (Mayo Clinic)

Because there are so many possible causes of fatigue, the doctor will likely ask you a number of questions about your lifestyle, possible sources of stress, and medications you are taking. He or she will also want to know more about the nature of your fatigue, including when it started and if it gets worse at certain times of the day.

If your doctor suspects an underlying medical condition, he or she may order one or more tests to diagnose it and develop a plan for treatment. Typical tests include blood and urine tests, as well as those that test kidney, liver, and thyroid function.

When Should You Go to the Emergency Room?

While fatigue itself is not a medical emergency, you should go to the hospital right away if you experience any of the following symptoms in addition to fatigue:

  • rectal bleeding
  • vomiting blood
  • a severe headache
  • pain in the chest area
  • a feeling of faintness
  • rapid heart beat
  • irregular heart beat
  • feeling short of breath
  • severe pain in the abdominal, back, or pelvic region
  • thoughts of suicide or self-harm
  • thoughts of harming another person

What Are Some Lifestyle Changes That Can Help Reduce Fatigue

There are a number of measures that can help lessen fatigue caused by a less-than-ideal lifestyle. If you are fatigued because of the way that you have been living, you should make changes to:

  • practice healthy eating habits and stay hydrated
  • exercise on a regular basis
  • get adequate sleep
  • take part in relaxing activities, such as yoga
  • avoid known stressors
  • avoid a work or social schedule that is overly demanding
  • live a smoke-free lifestyle
  • abstain from alcohol and drug use

These lifestyle changes—together with your doctor’s treatment plan for any health issues that may be causing your condition—can help ease your fatigue. Remember that although fatigue is a common symptom and complaint, it can take a physical and emotional toll on you if left untreated.

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See a list of possible causes in order from the most common to the least.


CFS (Chronic Fatigue Syndrome)

Chronic fatigue syndrome (CFS) is a debilitating disorder characterized by extreme tiredness that can't be explained by an underlying medical condition.

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Common colds and influenza are contagious infections that affect the respiratory system. Both are airborne illnesses, spread through coughing and sneezing. Shared symptoms include headache, cough, sore throat, and more.

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What is Fibromyalgia?

Fibromyalgia is a chronic disorder characterized by widespread, unexplained pain in tender points in muscles and joints, including the head, neck, and sides of hips.

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Congestive Heart Failure (CHF)

Congestive heart failure (CHF) is a chronic condition that affects the chambers of your heart. CHF refers to fluid buildup around your heart.

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Heart Failure

Right-side heart failure occurs when the right ventricle can't properly pump blood to your lungs to collect oxygen. Excessive fatigue, shortness of breath and abdominal bloating are signs.

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Chronic Bronchitis

People often develop acute bronchitis after a viral chest infection. Blue-colored lips ankle or foot swelling can result.

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Low Blood Sugar (Hypoglycemia)

This condition is considered a medical emergency. Urgent care may be required.

Also known as hypoglycemia, low blood sugar can be a dangerous condition. Hypoglycemia is rare in people who are not suffering from diabetes, the chronic disease that affects the body's ability to regulate blood sugar...

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Bipolar Disorder

Bipolar disorder mental illness marked by extreme from mania to depression. Bipolar disorder is also called bipolar disease or manic depression.

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Anorexia Nervosa

Anorexia is an eating disorder in which obsessive worry about body weight and the food you eat can result in severe weight loss. Symptoms include constipation, missed period, and thinning hair.

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Primary Hypothyroidism

Your thyroid gland controls the metabolism of all your cells. Your pituitary gland releases a hormone known as TSH (thyroid stimulating hormone) to stimulate your thyroid. Your thyroid then releases two hormones, T3 an...

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Low Blood Potassium

Hypokalemia occurs when the blood's potassium levels are too low. A normal level of potassium is 3.6-5.2 millimoles per liter. Levels below 3.6 are considered low.

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Low Blood Sodium (Hyponatremia)

Low blood sodium, or hyponatremia, occurs when water and sodium are out of balance in your body. A quick drop in sodium levels can cause weakness, headache, nausea, and muscle cramps.

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Congestive (Dilated) Cardiomyopathy

Congestive cardiomyopathy, also known as dilated cardiomyopathy, is characterized by a weak primary pumping chamber in the heart. Your heart automatically attempts to correct for this inefficiency. In turn, thi...

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Failure to Thrive

Your child may be diagnosed with failure to thrive if he or she falls below a healthy weight and shows signs of emotional underdevelopment. Typically, failure to thrive is discovered during a child's infant years. Idea...

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Obesity is defined as having a body mass index (BMI) of 30 or more. BMI is calculated using a person's weight and height. It can lead to other conditions like diabetes, heart disease, and cancer.

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Sleeplessness, or insomnia, is a serious sleep disorder. It can mean the inability to fall asleep or stay asleep throughout the night, or the tendency to wake too early before having gotten enough sleep.

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This feature is for informational purposes only and should not be used to diagnose.
Please consult a healthcare professional if you have health concerns.