Diagnosis requires that the patient have the following three symptoms*:
A substantial reduction or impairment in the ability to engage in pre-illness levels of occupational, educational, social, or personal activities that 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.
Post-exertional malaise - Worsening of a patient's symptoms and function after exposure to physical or cognitive stressors that were normally tolerated before disease onset.
At least one of the two following manifestations is also required*:
Cognitive impairment - Problems with thinking or executive function exacerbated by exertion, effort, or stress or time pressure.
Orthostatic intolerance - Worsening of symptoms upon assuming and maintaining upright posture. Symptoms are improved, although not necessarily abolished, by lying back down or elevating the feet.
ME/CFS: myalgic encephalomyelitis/chronic fatigue syndrome. * Frequency and severity of symptoms should be assessed. The diagnosis of ME/CFS should be questioned if patients do not have these symptoms at least half of the time with moderate, substantial, or severe intensity.