What Causes Fatigue: Chronic Fatigue

Content provided by the Faculty of the Harvard Medical School

What causes fatigue?

The cause of fatigue is not always obvious (see Figure 4). If you have the flu, you expect to feel tired. Or you may want to nap after a big lunch. But you may feel inexplicably groggy throughout the day, not just during the biological trough that normally occurs in mid-afternoon. Your doctor may find nothing wrong, leaving you to wonder if your symptoms are "all in your head."

Figure 4: Causes of fatigue Some causes of fatigue are obvious, such as lack of sleep or a medical illness, but many others are harder to pinpoint. Depression or anxiety, overwork, sedentary living, nutritional factors, even a medication could contribute to fatigue or cause a feeling of low energy.

The underlying cause of persistent fatigue can be hard to identify, but that doesn't mean the fatigue is imaginary. Fatigue often signals that something is wrong, physically or emotionally, or even with the pace and tempo of your daily schedule. The following are the most common causes of an ongoing lack of energy.

Last updated:	January 23, 2007