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What causes lethargy? 45 possible conditions

What Does Lethargy Mean?

Lethargy is a symptom that causes you to feel sleepy or fatigued and sluggish. This sluggishness may be in terms of movements or in thinking. You’re described as lethargic if you have these symptoms.

Lethargy can be related to an underlying physical or mental condition.

What Are the Symptoms of Lethargy?

Lethargy can cause some or all of the following symptoms:

  • changes in mood
  • decreased alertness/ability to think
  • fatigue
  • low energy
  • sluggishness

People with lethargy may act as if they are in a daze. They may move more slowly than they usually do.

What Causes Lethargy?

Many kinds of acute illnesses can make you feel lethargic. This includes the flu or a stomach virus. Other physical medical conditions can also cause lethargy. These include:

  • carbon monoxide poisoning
  • dehydration
  • hyperthyroidism
  • hypothyroidism
  • hydrocephalus (brain swelling)
  • kidney failure
  • Lyme disease
  • meningitis
  • pituitary diseases, such as pituitary cancer
  • poor nutrition
  • sleep apnea
  • stroke
  • traumatic brain injury
  • fever

Lethargy can be the result of mental health-related medical conditions. These include:

  • major depression
  • postpartum depression
  • premenstrual syndrome (PMS)

Lethargy can also be a side effect of taking certain medications. Taking narcotic medications can cause lethargy. You shouldn’t exceed your recommended dosage for this reason.

When Do I Seek Medical Help for Lethargy?

Lethargy can be a symptom that requires emergency medical attention. This is especially true if lethargy symptoms come on suddenly. Additional symptoms that may require emergency medical attention:

  • chest pain
  • unresponsiveness or minimally responsiveness
  • inability to move the limbs on one side of the body
  • disorientation (e.g., not knowing date, name, or location)
  • fast heartbeat
  • facial drooping on one side
  • loss of consciousness
  • rectal bleeding
  • severe headache
  • shortness of breath
  • vomiting blood

Any noticeable, marked changes in behavior accompanied by lethargy are often cause for concern. Seek immediate medical attention if you experience thoughts of harming yourself as well as lethargy.

Babies or young children can also experience lethargy. Symptoms in babies that may need immediate medical attention include:

  • difficult to rouse
  • fever greater than 102 degrees Fahrenheit
  • dehydration symptoms, such as crying without tears, dry mouth, or few wet diapers
  • sudden rash
  • vomiting forcefully, especially for more than 12 hours

You may also want to make an appointment at your doctor’s office if you have any of these symptoms as well as lethargy:

  • aches and pains that don’t go away with treatment
  • difficulty sleeping
  • difficulty tolerating hot or cold temperatures
  • eye irritation
  • fatigue that lasts longer than two weeks
  • feeling sad or empty frequently
  • irritability
  • swollen neck glands
  • unexplained weight gain or loss

How Is Lethargy Diagnosed?

Your doctor will often take a full medical history and then do a physical exam to figure out why you are experiencing lethargy. Obtaining a medical history includes discussing any medical conditions you may have previously experienced. The medical examination may include listening to your heart and lungs, testing for bowel sounds, and evaluating your mental awareness.

Diagnostic testing typically depends on what the doctor suspects may be an underlying cause. For example, if a thyroid disorder is suspected, your doctor may order blood tests to determine if your thyroid hormones are high or low.

Your doctor may order imaging studies if they suspect a head injury, stroke, meningitis, or other brain-related disorder is the cause. The imaging studies could include a computed tomography (CT) or magnetic resonance imaging (MRI) scan to determine if there are any abnormalities in the brain.

How Is Lethargy Treated?

Treatment for lethargy depends upon its underlying cause. Your doctor may prescribe medications to resolve an infection or to increase thyroid hormones. They may prescribe antidepressants if depression or another mental health-related disorder is the cause.

Remember that you can practice healthy habits at home to reduce fatigue-related symptoms if you experience lethargy. Examples include:

  • drinking plenty of fluids
  • eating a healthy diet
  • getting plenty of sleep
  • reducing stress levels

See a doctor if these healthy habits don’t help your symptoms go away.

Article Sources:

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


CFS (Chronic Fatigue Syndrome)

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Swine Flu

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PMS (Premenstrual Syndrome)

PMS symptoms start five to 11 days before menstruation and typically go away once menstruation begins. The cause of PMS is unknown.

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Dehydration occurs when you lose more fluid than you drink. The most common cause of water loss from the body is excessive sweating. Headaches, dizziness, and decreased urination are symptoms.

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Anorexia Nervosa

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Subdural Hematoma

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A subdural hematoma occurs when blood collects on your brain's surface beneath the skull. They usually result from a head injury.

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Hypovolemic Shock

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

Hypovolemic shock (hemorrhagic shock) is a life-threatening condition that results when you lose more than 20 percent of your body's blood or fluid supply, preventing the heart from pumping sufficient blood to your body.

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Cardiogenic Shock

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

Cardiogenic shock is a rare condition in which the heart is so damaged that it is unable to supply sufficient blood to bodily organs. Sweating and cold extremities are potential signs of this condition.

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Postpartum Depression

Postpartum depression affects as many as 13 percent of new mothers. In the U.S., that's half a million women. Learn about symptoms, causes, risks, and more.

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Diabetes Insipidus

Diabetes insipidus (DI) is a rare condition that occurs when your kidneys are not able to conserve water. It results in extreme thirst for water and frequent urination. There are several types of DI, and they can ofte...

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Sleep Apnea

Sleep apnea is a sleep disorder where breathing sporadically and repeatedly stops and starts while a person sleeps. Learn about the causes and treatments for sleep apnea now.

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Seasonal Affective Disorder

Seasonal affective disorder (SAD) is a form of depression. People affected by SAD display symptoms of depression at the same time every year, typically during the fall and winter months. According to the America...

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Kwashiorkor is a form of malnutrition caused by protein deficiency. It is the most common nutritional disorder in developing countries. Common symptoms are change in skin tone, diarrhea, flaky rash, and more.

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Shaken Baby Syndrome

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

Shaken baby syndrome is caused by forcefully and violently shaking a baby. Other names for this condition include abusive head trauma, shaken impact syndrome, whiplash shake syndrome, and inflicted head injury. Shake...

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Necrotizing Enterocolitis

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

Necrotizing enterocolitis is inflammation and death of intestinal tissue. It may involve just the lining or the entire thickness of the intestine. This very dangerous disease is most common in premature infants.

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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.