Lethargy Explained

Medically Reviewed By Megan Soliman, MD

Lethargy is a condition with characteristics such as drowsiness and an unusual lack of energy or mental alertness. It is often due to various medical or psychological conditions and lifestyle factors. This article will define lethargy. It will also discuss its symptoms and causes. Finally, it will talk about when to contact a doctor and how to treat lethargy.

What is lethargy?

Female lying bed with a yawning dog
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Lethargy is tiredness, drowsiness, or lack of energy. It sometimes accompanies depression, decreased motivation, or apathy. Lethargy can be a typical response to:

  • inadequate sleep
  • overexertion or stress
  • lack of exercise
  • boredom

When part of a typical response, lethargy often resolves with:

  • rest
  • adequate sleep
  • decreased stress
  • proper nutrition

Persistent lethargy that does not resolve with self-care may indicate an underlying physical or psychological condition.

The cause of lethargy may be clear based on its pattern and accompanying symptoms. If it starts in the morning and lasts all day, it could be due to depression or a lack of sleep. Lethargy may result from an underactive thyroid gland if it develops as the day passes and it accompanies:

Shortness of breath alongside lethargy may be due to heart or lung problems. Persistent lethargy with no clear diagnosis may result from chronic fatigue syndrome, which can start with a flu-like illness and often does not resolve with rest.

Lethargy by itself is rarely an emergency. However, it may require immediate evaluation if it develops suddenly or accompanies other serious symptoms. Prompt treatment can help prevent complications. Seek immediate medical care for:

  • sudden energy loss
  • dizziness or confusion
  • chest pain
  • blurred vision
  • high fever
  • decreased urine output
  • sudden swelling or weight gain
  • shortness of breath
  • rapid heart rate
  • altered level of consciousness
  • severe pain

If your lethargy is persistent or causes concern, contact your doctor.

What other symptoms might occur with lethargy?

Lethargy may accompany other symptoms, depending on the underlying condition. Identifying other symptoms may help determine its cause.

Heart and lung symptoms that may occur along with lethargy

Lethargy may accompany other symptoms affecting the heart or lungs, including:

Other symptoms that may occur along with lethargy

Lethargy may accompany symptoms related to other body systems, including:

  • anxiety or depressed mood
  • appetite changes
  • changes in bowel movements
  • changes in urination
  • fever
  • excess thirst
  • hair loss
  • musculoskeletal pain
  • skin changes
  • sneezing
  • unintentional weight gain or loss
  • weakness


Is there a difference between lethargy and fatigue?


Fatigue is sometimes an isolated symptom, while lethargy is more complex and can include many symptoms, including fatigue, decreased sense of alertness, drowsiness, and pronounced lack of energy.

Megan Soliman, MD Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.

Learn about fatigue.

What causes lethargy?

There are many possible causes of lethargy. These include underlying medical or psychological conditions and lifestyle factors.

Medical conditions

Various medical conditions can cause you to feel lethargic. These conditions include:

  • Anemia: This condition involves low levels of iron in your blood.
  • Sleep apnea: This condition affects your breathing while you are sleeping.
  • Hypothyroidism: This is an underactive thyroid gland. It causes insufficient thyroxine levels in your body.
  • Celiac disease: This is an autoimmune disorder that produces an allergic reaction to gluten.
  • Diabetes: This is a common condition wherein your body either does not produce enough insulin or cannot use it properly.
  • Chronic fatigue syndrome: This condition causes severe and disabling fatigue for at least 4 months.
  • Glandular fever: This illness results from a virus and can involve a sore throat and swollen glands.
  • Restless leg syndrome: This condition causes you to feel the need to constantly move your legs at night.
  • Cancer: Different cancer types and their treatments may cause you to experience lethargy.
  • Heart disease: Heart disease can make you feel lethargic as your heart may be working harder.
  • Kidney or liver problems: Issues with your kidneys or liver may cause you to feel lethargic.
  • Multiple sclerosis: This is a disease of the central nervous system that impacts your brain, spinal cord, and optic nerves.

Psychological conditions

Certain psychological conditions may cause lethargy. These conditions include:

  • Depression: This condition involves prolonged feelings of sadness, hopelessness, and dejection. It often causes lethargy or fatigue.
  • Anxiety and stress: Constant feelings of anxiety or stress can keep your body in overdrive. This constant supply of adrenaline can exhaust your body and lead to lethargy.
  • Grief: The loss of a loved one causes many emotions, leading to feelings of lethargy.

Learn about stress management tips.

Lifestyle factors

Many lifestyle factors can cause lethargy and tiredness. These factors include:

  • alcohol consumption
  • frequency and intensity of exercise
  • caffeine consumption
  • daytime naps
  • lack of nutrition

When should you see a doctor for lethargy?

Lethargy itself is not typically a cause for concern. However, contact your doctor if you experience lethargy or fatigue lasting more than 2 weeks.

If you experience any of the following symptoms, contact your doctor. These symptoms may be a sign of a more serious condition:

  • sudden loss of consciousness
  • shortness of breath
  • chest pain
  • clammy or pale skin
  • rapid heart rate
  • slurred speech or difficulty speaking
  • severe pain
  • difficulty controlling your facial muscles
  • difficulty moving your arms or legs

How is lethargy treated?

The treatment of lethargy depends largely on the underlying cause of it. Once your doctor can diagnose the cause, they will be able to recommend the most effective treatment for you.

If lethargy is not due to an underlying condition, there are ways you can manage it yourself. These include:

  • getting plenty of sleep
  • getting regular exercise or physical activity
  • eating a healthy and balanced diet
  • maintaining a moderate weight
  • reducing your stress where possible
  • reducing your caffeine intake
  • reducing your alcohol consumption
  • increasing your water intake


Lethargy is a condition that involves drowsiness and an unusual lack of energy or mental alertness. Various medical and psychological conditions can cause lethargy. Certain lifestyle factors, such as lack of sleep, nutrition, and high caffeine intake, can also result in lethargy.

If you experience persistent lethargy for more than 2 weeks, or if the lethargy concerns you, contact your doctor.

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Medical Reviewer: Megan Soliman, MD
Last Review Date: 2022 Sep 21
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THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.