The most prominent symptom of chronic fatigue syndrome is an unexplained feeling of fatigue, which is not relieved by rest. This fatigue is severe enough to decrease a person's activity level at home, work or school by 50% or more. In addition, the diagnosis requires that patients should have at least four of the following symptoms that also are present for at least six months:
Impaired concentration or short-term memory, severe enough to affect routine activities at home, work, school or social functions
Enlarged lymph nodes (swollen glands) in the neck or underarm area
Pain in several joints, with no redness or swelling
Headaches that are different in some way: a new type of headache pain, a new pattern of headaches or headaches that are more severe than before
Sleep that doesn't refresh, or not feeling rested on waking
An extreme reaction to exertion: feeling sick after exercise or strenuous activity, often not starting until the next day
People with chronic fatigue syndrome often have other symptoms that are not part of the official definition of the illness, such as nausea and difficulty tolerating alcoholic beverages or medicines that act on the brain. Many people also have allergies, such as hay fever (allergic rhinitis) or recurring sinus problems.
About half of people with chronic fatigue syndrome develop depression in the months and years after their illness starts. However, available evidence indicates that chronic fatigue syndrome is not a psychiatric illness. Rather, it appears to be a physical illness that leads to depression in some people.