Why You May Be Dealing With Lethargy

women tired at her desk

Kathrin Ziegler / Getty Images

Table of Contents
View All
Table of Contents

Lethargy is a condition characterized by fatigue, drowsiness, and an unusual lack of energy and mental alertness. Lethargy is not a medical condition in itself, but it may be a symptom of a health condition, or a natural response to lack of sleep, stress, or poor eating habits.

In medical or hospital settings, the term lethargy denotes a patient’s inability to stay awake or engage in any type of interaction, says Paula Zimbrean, MD, a psychiatrist at Yale Medicine. “It is often associated with severe illness or with sedating medications, such as painkillers.”

This article explores the causes and characteristics of lethargy, as well some steps that can help you identify and treat its underlying causes.

Characteristics of Lethargy

Lethargy can make it hard for you to get out of bed in the morning and go about your day. These are some of the characteristics of lethargy, according to Dr. Zimbrean:

  • Profound fatigue that is disproportionate to your activity levels
  • Persistent feeling of tiredness and lack of energy
  • Sluggishness or a feeling of moving in slow motion
  • Frequent need to sit down and rest
  • Drowsiness and increased need for sleep
  • Muscle stiffness or weakness
  • Headaches or muscle pains
  • Malaise, or a general feeling of discomfort
  • Changes in appetite
  • Lack of initiative or motivation
  • Lack of interest and enthusiasm
  • Lack of attention and alertness
  • Difficulty paying attention, making decisions, or recalling things

Causes of Lethargy

The causes of lethargy can be medical or lifestyle-related. 

Medical Causes of Lethargy

Many medical problems, ranging from infection to cancer, can cause lethargy, says Dr. Zimbrean. These are some of the potential medical causes of lethargy and fatigue:

  • Infections, including the flu, COVID-19, parasitic infections, hepatitis, human immunodeficiency virus (HIV), tuberculosis, and mononucleosis
  • Diseases, including kidney disease, liver disease, multiple sclerosis, and cancer
  • Autoimmune disorders, including lupus and rheumatoid arthritis
  • Chronic conditions, including diabetes, fibromyalgia, and chronic pain
  • Heart problems, including heart disease, heart failure, and postural orthostatic tachycardia syndrome
  • Lung conditions, including emphysema and chronic obstructive pulmonary disease (COPD)
  • Hormonal imbalances, including thyroid conditions and Addison disease
  • Sleep disorders, including narcolepsy, obstructive sleep apnea, and insomnia
  • Injuries, such as bone fractures or tissue injuries
  • Nutrient deficiencies, including anemia, dehydration, malnutrition, and vitamin B12 and vitamin D deficiencies
  • Mental health conditions, including depression, grief, and anxiety
  • Eating disorders and weight issues, including bulimia, anorexia, obesity, and being underweight
  • Medications, including sleeping pills, blood pressure medications, painkillers, antidepressants, antihistamines for allergies, steroids, and diuretics (water pills)
  • Treatments, including chemotherapy and bone marrow transplants

Lethargy often appears before the onset of other physical symptoms, such as pain or fever, and persists after the other symptoms have resolved, says Dr. Zimbrean.

Lifestyle-Related Causes of Lethargy

These are some of the lifestyle-related causes of lethargy and fatigue:

  • Insufficient or excess sleep: Adults generally need around seven to nine hours of sleep every night. Sleeping only a few hours every night or sleeping over 11 hours every night can contribute to lethargy.
  • Shift work: Your body is naturally programmed to be active during the day and sleep in the night. Working night shifts or switching between day and night shifts can upset your circadian rhythm.
  • Substance use: Substances like alcohol, nicotine, and cannabinoids can disrupt your sleep patterns or cause insomnia.
  • Sedentary lifestyle: Exercise not only helps you stay mentally and physically fit, it also helps you get a good night’s sleep.
  • Poor diet: Your body needs a healthy, balanced diet to meet all its nutritive needs. A poor diet can cause nutritional deficiencies which can result in lethargy. Some low-carb diets can also contribute to lethargy, because carbs are the body’s main source of fuel. Sugary foods or refined carbs don’t help either; they offer a quick spike of energy and then a crash that leaves you lethargic, low on energy, and hungry. 

Diagnosing the Causes of Lethargy

If you can’t seem to shake the feeling of lethargy, Dr. Zimbrean says the first step is to ensure that you’re getting enough restful sleep. “Try to eliminate sleep interruptions and any sedatives.” 

However, if you’re getting adequate sleep every night and aren’t taking any sedatives, Dr. Zimbrean recommends visiting your primary care doctor.

These are some steps your doctor may take, to identify the cause of the lethargy, according to Dr. Zimbrean:

  • Take a complete personal and family medical history.
  • Ask you about when you started noticing the lethargy, what it feels like, and what other symptoms you are experiencing.
  • Review any medications you are taking.
  • Determine whether you are using any substances.
  • Perform a physical exam and run some tests. Physicians generally try to start with the least disruptive and invasive tests first. For instance, your healthcare provider may start with some blood tests and an electrocardiogram. Depending on the initial results, more studies may be needed, such as sleep studies, ultrasounds, biopsies, or computed tomographies. 

These steps can help your healthcare provider determine whether you have an underlying health condition that is causing you to feel lethargic.

It can be helpful to do a self-check on your lifestyle to identify potential culprits and work with your doctor to identify the cause of the lethargy, says Dr. Zimbrean.

Treating the Causes of Lethargy

If the lethargy is related to sleep disruptions, it can be helpful to work toward building a consistent routine with adequate, restful sleep. 

If the lethargy is caused by another health condition, it’s important to treat the underlying cause, says Dr. Zimbrean. Your healthcare provider will work with you to chart the best course of treatment, depending on the health condition, the symptoms you're experiencing, your medical history, and your circumstances and preferences.

If lethargy persists after the cause is being treated, medications known as stimulants are sometimes used, says Dr. Zimbrean. “A good old cup of coffee may help too if there are no medical contraindications.”

Coping With Lethargy

Dr. Zimbrean shares some strategies that can help you cope with lethargy:

  • Adjust your schedule: Try to adjust your schedule—and your expectations—to accommodate shorter bouts of activity, so you can take breaks and get some rest.
  • Inform loved ones: Speak to your family and let them know how you’re feeling, so they understand that your low energy levels and lack of participation are not a result of disinterest.
  • Get some exercise: Paradoxically, exercise can help increase your energy levels. Start with whatever you can do. Even a little at a time, such as a 10-minute walk every day, can go a long way.
  • Avoid substances: Refrain from quick fixes and substances such as alcohol, nicotine, cocaine, or other drugs.
  • Maintain a healthy routine: Work on maintaining a consistent and balanced daily routine, with a reasonable work and personal schedule, adequate sleep, and a nutritious diet.

A Word From Verywell

Feeling lethargic can cause you to feel like you’re moving around in a daze. It can make it hard for you to function, or be interested or attentive. 

Lethargy isn’t a medical condition or a medical emergency; however, it could be a sign of stress, inadequate sleep, poor nutrition, or a health condition. If it persists, it’s important to visit a healthcare provider to identify and treat its cause.

8 Sources
Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. National Cancer Institute. Lethargy. NCI's Dictionary of Cancer Terms.

  2. National Library of Medicine. Fatigue. Medline Plus.

  3. Cleveland Clinic. Fatigue.

  4. Davis MP, Goforth H. Fighting insomnia and battling lethargy: The yin and yang of palliative care. Curr Oncol Rep. 2014;16(4):377. doi:10.1007/s11912-014-0377-1

  5. Grubbs JJ, Raizen DM. Sleep: AMPs mediate injury-induced lethargy. Curr Biol. 2021;31(3):R131-R133. doi:10.1016/j.cub.2020.11.048

  6. Department of Health, State Government of Victoria. Fatigue.

  7. Centers for Disease Control and Prevention. How much sleep do I need?

  8. National Library of Medicine. Carbohydrates. Medline Plus.

By Sanjana Gupta
Sanjana is a health writer and editor. Her work spans various health-related topics, including mental health, fitness, nutrition, and wellness.