What is "orthostatic hypotension"

n. low blood pressure occurring in some people when they stand up [syn: postural hypotension]

Orthostatic hypotension, also known as postural hypotension, orthostasis, and colloquially as head rush or dizzy spell, is a form of low blood pressure in which a person's blood pressure falls when suddenly standing up or stretching. In medical terms, it is defined as a fall in systolic blood pressure of at least 20 mm Hg or diastolic blood pressure of at least 10 mm Hg when a person assumes a standing position.

The symptom is caused by blood pooling in the lower extremities upon a change in body position. It is quite common and can occur briefly in anyone, although it is prevalent in particular among the elderly, and those with low blood pressure.