1. Health
You can opt-out at any time. Please refer to our privacy policy for contact information.

Discuss in my forum

What Is Fatigue?

Insomnia and Other Medical Conditions May Be the Cause


Updated November 29, 2012

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

It may seem like a word game of semantics, but how does fatigue differ from sleepiness? What exactly is fatigue? Is it an important distinction? What causes fatigue? Learn about fatigue or tiredness and what medical conditions it may suggest.

Defining Fatigue

Fatigue or tiredness should be distinguished from words like sleepiness or drowsiness. Fatigue is a perceived lack of energy. It may represent mental or physical exhaustion. Some relate fatigue to an extreme tiredness felt deep within the muscles and bones after profound exertion. For example, if you run a marathon, your muscles will feel fatigued. It may also occur in the context of acute or chronic illness.

Fatigue is not a desire to fall asleep. This is best described as sleepiness, a condition that results from the gradual accumulation within the brain of a natural chemical called adenosine. Many people with complaints of fatigue are not excessively sleepy and, conversely, those with excessive daytime sleepiness may not feel drained of energy.

What Conditions Cause Fatigue?

There are a variety of conditions that may result in fatigue. It is a common complaint of people with insomnia. Insomniacs are notorious for feeling run down during the day, but if given an opportunity to nap, they cannot. It may also occur in numerous other medical conditions, including anemia, hypothyroidism, depression, or even cancer. If persistent without a clear cause, it may be diagnosed as chronic fatigue syndrome.

If you are struggling with fatigue, you may wish to start by speaking with your doctor about your concern. Certain tests may be indicated to rule out other causes of your fatigue. There are also measures to take to conserve energy in extreme fatigue. If it is determined that you are instead suffering from sleepiness, a difference in terms and causes, an evaluation for disorders such as sleep apnea may be indicated.

  1. About.com
  2. Health
  3. Sleep
  4. Sleep Disorder Basics
  5. What Is Fatigue

©2014 About.com. All rights reserved.

We comply with the HONcode standard
for trustworthy health
information: verify here.