Orthostatic intolerance

Prevalence
Orthostatic intolerance is a commonly dysfunction in ME/CFS Estimates of the rate of orthostatic intolerance in chronic fatigue syndrome and myalgic encephalomyelitis patients vary widely, with estimates as low as 50% to as high as 97% of patients.

Orthostatic intolerance is also commonly associated with fibromyalgia

Orthostatic intolerance is diagnosed by a tilt table test. It is part of the Institute of Medicine report's proposed diagnostic criteria for systemic exertion intolerance disorder.

Postural orthostatic tachycardia
Postural orthostatic tachycardia syndrome (POTS) is one of a group of disorders that have orthostatic intolerance (OI) as their primary symptom.