Chronic fatigue syndrome, also called chronic fatigue and immune dysfunction syndrome, is a condition in which a person experiences severe symptoms of persistent fatigue and malaise (feeling like one has the flu). These symptoms must last for a prolonged period of time, usually more than six months, before a diagnosis of chronic fatigue syndrome is made. The symptoms of this disorder can vary and are sometimes difficult to pinpoint.

The primary symptom of this condition is fatigue. This is persistent fatigue that does not go away with rest. Malaise, or flu like feeling, may accompany this fatigue. The severity varies from person to person and may range anywhere from a mild tired feeling to completely bedridden. Many people with this syndrome however, are limited in their ability to complete daily activities.

Other symptoms of chronic fatigue syndrome include muscle and joint pain, recurrent sore throat, swollen lymph nodes, irritable bowel, periods of low blood pressure, sleep disturbances, low blood pressure, headaches, depression, and difficulty regulating body temperature. All of these symptoms vary in presence and degree of severity from person to person.

Based on current research, chronic fatigue syndrome appears to be a disease that stands on its own, rather than a condition related to other diseases. The actual cause of the disease is still unknown, but research points to mechanisms in both the central nervous system and the immune system building upon each other as the ultimate cause of this condition. Chronic fatigue syndrome does have some aspects in common with fibromyalgia and some possible disease mechanisms in common as well, so these two diseases may be related. The research on this is still inconclusive.

Chronic fatigue syndrome usually occurs suddenly, often after an episode of flu or bronchitis. It usually occurs in people age 40 to 50 and occurs most often in women. While this disease is not fatal, the outlook for recovery is also not optimistic.

Treatment for this disease usually focuses on learning to adjust a person's lifestyle to live with the symptoms. Medications may be prescribed to address individual symptoms. Physical and occupational therapies to address exercise, activity pacing, adaptations, and other lifestyle changes are also often prescribed. Counseling and behavior therapy may be needed, especially if a person is experiencing cognitive symptoms such as brain fog. Alternative therapies like acupuncture may also be helpful, but should be attempted under guidance of a physician.