The Institute of Medicine of the National Academies has proposed the following diagnostic criteria for myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS):

1. A substantial reduction or impairment in the ability to engage in pre-illness levels of occupational, educational, social or personal activities, which persists for more than six months and is accompanied by fatigue, which is often profound, is of new or definite onset (not lifelong), is not the result of ongoing excessive exertion and is not substantially alleviated by rest, and,

2. Post-exertional malaise and

3. Unrefreshing sleep

At least one of two manifestations is also required:

1. Cognitive impairment

2. Orthostatic intolerance (symptoms worsen upon standing and are relieved when lying down)

Other ME/CFS symptoms:

Pain (common, but variable in nature and severity)

Certain infections may be triggers

Gastrointestinal and urinary problems

Sore or scratchy throat

Painful or tender axillary/cervical lymph nodes

Sensitivity to light, sound, noise and other external stimuli

Source: Institute of Medicine of the National Academies