For many years Chronic Fatigue Syndrome (CFS) was misunderstood by the medical community, as it has numerous symptoms that could also be mistaken for other conditions. Also in many cases, physicians could not find any cause for the symptoms.

According to the Center for Disease Control, there are two criteria for CFS:
1. Have severe chronic fatigue of six months or longer duration with other known medical conditions excluded by clinical diagnosis; and
2. Concurrently have four or more of the following symptoms: substantial impairment in short-term memory or concentration; sore throat; tender lymph nodes; muscle pain; multi-joint pain without swelling or redness; headaches of a new type, pattern or severity; unrefreshing sleep; and post-exertional malaise lasting more than 24 hours. The symptoms must have persisted or recurred during six or more consecutive months of illness and must not have predated the fatigue.

Additional symptoms may include abdominal pain, alcohol intolerance, bloating, chest pain, chronic cough, diarrhea, dizziness, dry eyes or mouth, earaches, irregular heartbeat, jaw pain, morning stiffness, nausea, night sweats, psychological problems (depression, irritability, anxiety, panic attacks), shortness of breath, skin sensations, tingling sensations, and weight loss.

Chronic Fatigue Syndrome can affect individuals every age, gender, ethnicity and socioeconomic group. Women are affected four times more than men, but is most common among people in their 40's and 50's. Children can develop CFS during the teen years.