Chronic fatigue syndrome is a flu-like condition that can drain your energy and, sometimes, last for years. People previously healthy and full of energy may experience a variety of signs and symptoms.

People with chronic fatigue syndrome exhibit signs and symptoms similar to those of most common viral infections. Unlike flu (influenza) symptoms, which usually subside in a few days or weeks, the signs and symptoms of CFS can last much longer. They may come and go frequently with no identifiable pattern.

Primary signs and symptoms

In addition to persistent fatigue, not caused by other known medical conditions, chronic fatigue syndrome has eight possible primary signs and symptoms. Chronic fatigue syndrome symptoms include:

• Loss of memory or concentration

• Sore throat

• Painful and mildly enlarged lymph nodes in your neck or armpits

• Unexplained muscle soreness

• Pain that moves from one joint to another without swelling or redness

• Headache of a new type, pattern or severity

• Sleep disturbance

• Extreme exhaustion lasting more than 24 hours after physical or mental exercise

According to the International Chronic Fatigue Syndrome Study Group — a group of scientists, researchers and doctors brought together by the Centers for Disease Control and Prevention (CDC) to determine a standard method for defining and diagnosing chronic fatigue syndrome — a person meets the diagnostic criteria of chronic fatigue syndrome when unexplained persistent fatigue occurs for six months or more along with at least four of the eight primary signs and symptoms.

Additional signs and symptoms

In addition, people with chronic fatigue syndrome have reported other various signs and symptoms that aren't part of the official definition. These include:

• Abdominal pain

• Allergies or sensitivities to foods, alcohol, odors, chemicals, medications or noise

• Bloating

• Chest pain

• Chronic cough

• Diarrhea

• Dizziness, balance problems or fainting

• Dry mouth

• Earache

• Irregular heartbeat

• Jaw pain

• Morning stiffness

• Nausea

• Chills and night sweats

• Psychological problems, such as depression, irritability, anxiety disorders and panic attacks

• Shortness of breath

• Tingling sensations

• Visual disturbances, such as blurring, sensitivity to light, eye pain and dry eyes

• Weight loss or gain

The severity of symptoms

The severity of CFS/ME can roughly be divided into four levels:

• Mild cases - you can care for yourself and can do light domestic tasks, but with difficulty. You are still likely to be able to do a job, but may often take days off work. In order to remain in work you are likely to have stopped most leisure and social activities. Weekends or other days off from work are used to rest in order to cope.

• Moderate cases - you have reduced mobility and are restricted in most activities of daily living. The level of ability and severity of symptoms often varies from time to time ('peaks and troughs'). You are likely to have stopped work and require rest periods, often sleeping in the afternoon for one or two hours. Night-time sleep tends to be poor and disturbed.

• Severe cases - you are able to carry out only minimal daily tasks such as face washing and cleaning teeth. You are likely to have severe difficulties with some mental processes such as concentrating. You may be wheelchair dependent for mobility and may be unable to leave your home except on rare occasions, and usually have severe prolonged after-effects from effort.

• Very severe - you will be unable to mobilise or carry out any daily tasks for yourself and are in bed for the majority of the time. You are often unable to tolerate any noise, and are generally very sensitive to bright light.

Most cases are mild or moderate but up to 1 in 4 cases are severe or very severe.