Fatigue is a lack of energy or a feeling of debilitating tiredness. It affects almost everyone at some point. It can be a normal response to overexertion, stress or minor illness such as a cold. However, it can also be a symptom of a medical condition or signal that a disease has worsened.

Most people can recover from fatigue due to nonmedical origins in a short period of time. However, continually getting inadequate amounts and quality of sleep can create a sleep debt even in otherwise healthy people. Long-term sleep debt can cause health problems that require medical attention. Fatigue alone can also significantly influence the ability of people to function.

The many conditions that can cause fatigue include pain disorders, diabetes, heart disease, lung problems, mental conditions, digestive disorders or cancer. It may also be due to certain medications or other medical treatments.

Diagnosis typically begins with a review of the patient's medical history and a physical examination. Factors important in the history include current medical conditions, medications and pattern of fatigue.

Patients may be diagnosed with chronic fatigue syndrome if they have debilitating fatigue for at least six months and meet certain other criteria.

Treatment focuses on addressing the underlying cause of fatigue and achieving adequate rest. Possible options may include sleep therapy, exercise, or changes in diet or medication People can help prevent fatigue by getting regular medical care and practicing good health habits such as exercise, diet, stress management and regular sleep.