Five symptoms of myalgic encephalomyelitis/chronic fatigue syndrome include: 1. A substantial reduction or impairment in the ability to engage in pre-illness levels of occupational, educational, social or personal activities for longer than 6 months 2. Post-exertional malaise (PEM), which is a worsening of symptoms following physical, mental, or emotional exertion that would not have caused a problem before the illness. 3. Unrefreshing sleep that leaves not feeling better or perhaps even feeling worse after a full night’s sleep and no other reason for poor sleep quality. 4. Cognitive impairment, such as problems with thinking, memory, attention, organization skills, and information processing. 5. Orthostatic intolerance, which is a worsening of symptoms upon assuming and maintaining upright posture.

The main symptomatology is the presence of intense fatigue (tiredness) that worsens with physical or mental activity, but does not improve with rest. Other important symptoms are difficulty with memory or concentration, muscle and joint pain, headache and unrefreshing sleep.