An Overview of Lethargy and Possible Causes

Lethargy is not a symptom specific to any one particular disease. Rather, it could be a symptom of different diseases and health conditions. It can be a normal response to factors such as not getting enough sleep, stress, or eating poorly.

When lethargy develops as a response to various life situations, it resolves with rest, increased sleep, good nutrition, and being active. However, in the case of illness, lethargy can linger for days, weeks, or even months. Learn more about the causes, symptoms, and treatments for lethargy.

Lethargy has been described as unrelenting exhaustion that includes chronic fatigue, lack of energy, and sluggishness. People who are lethargic may also experience:

• Depression
• Apathy
• Lack of motivation
• Mild impairment of alertness
• Cognitive difficulties (forgetfulness and trouble concentrating)
• Severe drowsiness

Other symptoms that may accompany lethargy include:

• Aches and pains that won’t go away despite treatment
• Sleep problems
• Sensitivity to hot and cold temperatures
• Eye inflammation
• Chronic fatigue lasting more than two weeks
• Swollen neck glands
• Unexplained weight changes
• Often feeling sad, empty, or irritable

People who are lethargic may act as if they are in a daze. They may not move as quickly as they usually do and may be aware that they are in poor health.

Lethargy can be severe enough to affect consciousness. It may cause severe drowsiness—a person can still be alert, but then they drift off either into sleep or into a daze.

Lethargy has a number of causes. It can be the body’s response to not getting enough sleep, overexertion, stress, lack of activity, or improper nutrition. It can also be a side effect of medication or the body’s response to alcohol. Consumption of alcohol while on medication can also cause a person to feel lethargic.

Lethargy is a symptom of many acute (abrupt onset) conditions, including the flu, stomach viruses, fever, dehydration, and nutritional deficiencies. Other serious medical conditions that cause lethargy may include, but are not limited to:

• Carbon monoxide poisoning
• Hyperthyroidism (excess production of thyroid hormone)
• Hypothyroidism (insufficient production of thyroid hormone)
• Hydrocephalus (brain swelling) or brain injuries
• Kidney failure
• Meningitis
• Stroke
• Pituitary diseases (caused by too much or too little pituitary hormone)

Lethargy is rarely a medical emergency. However, it can become one if it is accompanied by other serious symptoms. It is important to seek immediate medical attention and call 911 for sudden energy loss, severe dizziness, chest pain, confusion, blurred vision, high fever, or sudden and severe swelling.

Other serious symptoms that require medical attention include:

• Shortness of breath
• Rapid heart rate
• Altered consciousness
• Severe pain
• Slurred speech
• Facial paralysis
• Inability to move arms and legs
• Severe headache

Significant changes in behavior with lethargy are concerning and may require medical attention. Seek urgent medical care if lethargy brings about thoughts of self-harm.

When lethargy is not a medical emergency, it may still require a doctor’s visit to determine the cause of it and other symptoms.  

Lethargy can also affect children and babies. Symptoms needing medical attention in young children and babies include difficulty with waking or appearing to be in a daze, weakness, fevers higher than 102 degrees Fahrenheit, dehydration (including reduced tears, dry mouth, and decreased urine output), rashes, and vomiting.

The first step in determining the cause of lethargy is to see a doctor or get immediate medical attention if necessary. Your doctor will work to determine the cause of lethargy and other symptoms. Diagnostic testing including blood work, urine tests, and imaging may be needed.

Once the cause of lethargy can be determined, treatment can begin or a referral to a specialist is made. Your doctor may also recommend seeing a specialist if the cause of lethargy and other symptoms cannot be established. Treatment and prognosis for lethargy will depend on the underlying cause.

If lethargy is caused by emotional or physical stress or exhaustion, it does not require medical treatment. It is often resolved by staying hydrated, getting enough sleep, maintaining a healthy diet, and managing stress.

Of course, there are instances in which lethargy will require medical treatment, especially when it is present with other very serious symptoms. In these instances, treatment is aimed at the underlying cause of the lethargy.

For instance, treatment of lethargy caused by dehydration is improved intravenous fluids and/or electrolyte consumption. Treatment for hyperthyroidism can resolve lethargy symptoms with anti-thyroid drugs, radioactive iodine, and beta blockers. 

Additional examples of treatments for lethargy include:

• Lethargy associated with inflammation: Treatment includes relieving inflammation with disease-modifying antirheumatic drugs (DMARDs), non-steroidal anti-inflammatory drugs (NSAIDs), and corticosteroids.
• Lethargy connected to depression: This can be treated by managing depressive symptoms, including with anti-depressants.
• Cancer-associated lethargy: Doctors may prescribe stimulant medications, such as Provigil (modafinil) for short periods. In addition, Provigil can increase wakefulness. Prescription sleep aids can also be prescribed if sleep issues are causing lethargy.

Healthy habits can also help you to manage the fatigue associated with lethargy. This includes staying hydrated, eating healthy foods, reducing stress, being active, and getting plenty of sleep.

Lethargy is usually not a medical emergency, but it can be a symptom of a serious health condition. Therefore, it is important to seek medical attention as soon as possible. Once the cause of lethargy is determined, it is important to follow the treatment plan prescribed by your doctor to feel better and reduce your risk for any potential complications.