What Is Fatigue and What Causes It?

By Ashley Ess in Healthy Feeling

With so much going on in our lives with work, family, and passion projects, it's hard not to get caught up in the whirlwind of nonstop doing. But what happens when all that doing leads you to frequently feel physically, mentally, and emotionally exhausted? When you're tapped out of energy, you may be suffering from fatigue. Learn more about how medical professionals define fatigue and how it affects us.

What Is Fatigue?

The Mayo Clinic defines fatigue as "a nearly constant state of weariness that develops over time and reduces your energy, motivation, and concentration." Fatigue can affect your emotional and psychological well-being, too.

Everyone experiences some level of fatigue on occasion, but temporary episodes usually have a specific cause and identifiable remedy, while unrelenting fatigue is not relieved by rest.

Woman Sleeping on Table

Causes of Fatigue

What is fatigue actually caused by? There are several factors that come into play when figuring out how to diagnose and combat fatigue. The Mayo Clinic states that there are two main categories for the causes of fatigue:

  • Lifestyle: Your lifestyle may have an impact on your energy levels if you don't get regular exercise, get too much exercise, sleep too few hours, or eat poorly.
  • Health conditions: An underlying medical condition—including stress, depression, and anxiety, as well as chronic conditions such as cancer and diabetes—can also lead to fatigue.


According to Harvard Medical School, fatigue can have a variety of effects. Your concentration or memory may be dull. The smallest tasks can feel like monumental feats. You may be easily agitated or irritated. All of these symptoms, among potentially many others, spell out that you might be fatigued.

We all have days when we are more tired than others, especially after an occasional grueling day at work or a busy day out with the family. But when you notice that the frequency of your exhaustion doesn't seem to let up, it's time to adjust your lifestyle to accommodate for some downtime.

Fatigue can also be a warning sign that more serious health problems may be occurring. Harvard Medical School specifies that conditions such as anemia, sleep problems, hypothyroidism (low thyroid hormone levels), and heart disease may cause fatigue, so it is vital to consult your doctor if you experience constant weariness.

Importance of Sleep

According to the National Safety Council, fatigue can have serious consequences beyond our physiological health. When you are sleep deprived, even sleeping fewer than seven hours in one 24-hour period, you are at greater risk of motor vehicle accidents.

The American Academy of Sleep Medicine and the Sleep Research Society have concluded through joint research that adults should get at least seven hours of sleep each night on a regular basis. When the body isn't given adequate time to rest and regenerate, you increase your risk of conditions such as diabetes, weight gain, and depression. If you are trying to make up for lost sleep or are recovering from an illness, nine or more hours of sleep can be appropriate. Be sure to talk to your healthcare provider for information on the number of sleep hours that is right for you.

Man Sleeping in Bed

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Why It's Good

Identifying the source of your fatigue early is the key to finding relief. Once you pinpoint the cause, you can be on your way to more restful nights and energetic days.