Extreme, debilitating exhaustion is the hallmark of chronic fatigue syndrome (CFS). People with CFS sleep poorly and awake unrefreshed. They have frequent headaches, muscle and joint pain, recurring sore throats, and memory and concentration problems. The intensity and type of symptoms can vary from day to day and from person to person. On a "good day" symptoms may be mild, and someone with CFS may be able to function at a near normal level. On a "bad day," they may be unable to get out of bed. Their condition is not improved by bed rest and can be worsened by mental activity.
Once dismissed as "yuppie flu" – a form of depression, stress and burnout common in young, upper income white women – CFS is now known to exist worldwide in every age, income bracket, and ethnic group, and in both sexes. CFS is about four times more common in women than in men, but that may be because women are more likely to report their symptoms to a doctor and it appears to be most prevalent in the 40 to 60 year age range.
The weariness, pain, and numerous other symptoms associated with CFS can frustrate both patient and physician. Because they do not cause visible and/or measurable abnormalities, it can be hard for friends, family and the public to understand the painful challenges faced by a person with CFS. It has also led to lingering scepticism about the existence of CFS despite the fact that all major health organisations now recognise it as a distinct medical condition. Some doctors attribute their patients' symptoms to depression or stress, or believe that they are simply symptoms of another, as yet undiagnosed, disease or disorder. Depression is a common consequence of CFS, but it is not a cause.
A large number of other diseases, disorders, and temporary conditions can cause or display similar symptoms or side effects. These include hypothyroidism, mononucleosis, psychological disorders, eating disorders, cancer, autoimmune disease, infections, drug or alcohol abuse, reactions to prescription medications, and – for whatever reason – insufficient uninterrupted sleep. In these cases, an underlying reason for the fatigue can be established and often treated. This temporary, short-term, or long-term fatigue must be distinguished from CFS.