Orthostatic Intolerance

blurry scene as if dizzy
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Orthostatic intolerance (OI) is an abnormal response to being upright that can cause dizziness and fainting. Typically, someone with this problem will be fine when seated or in a prone position, then they becomes dizzy upon standing. The term "orthostatic" comes from "orthostasis," which literally means standing up.

Orthostatic intolerance may also strike after strenuous exercise, and it's a common symptom of both fibromyalgia and chronic fatigue syndrome.

What Happens in the Body

In a healthy person, blood pressure increases when you stand up in order to combat the effects of gravity and keep blood going to your brain. In someone with OI, it's believed that the blood pressure drops and the heart rate increases. Abnormally low blood pressure briefly deprives the brain of blood and oxygen, causing lightheadedness.

Related Symptoms

OI may lead to other symptoms, including:

  • Headache
  • Visual disturbances (e.g., seeing spots, flashing lights)
  • Trembling
  • Sweating
  • Fatigue
  • Nausea
  • Problems with breathing or swallowing
  • Paleness of the face

In fibromyalgia and chronic fatigue syndrome, this symptom is thought to be the result of postural orthostatic tachycardia syndrome, or POTS, which is believed to stem from dysregulation in the autonomic nervous system, called dysautonomia.

Related to chronic fatigue syndrome, a 2011 study (Miwa) suggests that OI may be linked to a heart abnormality in which the left ventricle (one of the chambers of the heart) is smaller than normal.

Outside of illness, orthostatic intolerance can result from problems other than dysautonomia, such as dehydration.


Garland EM, Celedonio JE, Raj SR. Current neurology and neuroscience reports. 2015 Sep;15(9):60. Postural tachycardia syndrome: beyond orthostatic intolerance.

Miwa K. Heart vessels. 2015 Sep 15. [Epub ahead of print] Variability of postural orthostatic tachycardia in patients with myalgic encephalomyelitis and orthostatic intolerance.

Miwa K, Fujita M. Clinical cardiology. 2011 Dec;34(12):782-6. Small heart with low cardiac output for orthostatic intolerance in patients with chronic fatigue syndrome.

Vincent A, et al. Journal of clinical rheumatology. 2014 Mar;20(2):106-8. A report of the autonomic symptom profile in patients with fibromyalgia.

Yun DJ, Choi HN, Oh GS. Korean journal of pain. 2013 Jul;26(3):303-6. A case of postural orthostatic tachycardia syndrome associated with migraine and fibromyalgia.