A condition characterized by development of symptoms while standing. It is an autonomic nervous system disorder and the symptoms are relieved once the person sits back down. Symptoms include heart palpitations, sweating, anxiety, lightheadedness, hyperpnea, anxiety, and blurred vision.

A condition in which there is the presence of greater than or equal to 1 symptoms (e.g., dizziness, lightheadedness, nausea, dyspnea, vision change) occurring specifically when assuming or maintaining upright position and resolving in the seated or supine position.

Symptoms of cerebral hypoperfusion or autonomic overaction which develop while the subject is standing, but are relieved on recumbency. Types of this include NEUROCARDIOGENIC SYNCOPE; POSTURAL ORTHOSTATIC TACHYCARDIA SYNDROME; and neurogenic ORTHOSTATIC HYPOTENSION. (From Noseworthy, JH., Neurological Therapeutics Principles and Practice, 2007, p2575-2576)

Orthostatic intolerance is a confusing topic. Some of the confusion originates from recent appreciation of the condition's clinical variants, some originates from the emerging understanding of its diverse underlying pathophysiologies, and some originates from its nomenclature, which seems to change at least every year.