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Postural or orthostatic hypotension
In individuals who are dehydrated or anemic, blood pressure readings may be
normal when they are lying flat, however, the lack of fluid is unmasked when they
stand up quickly. The lack of blood to the brain causes dizziness and lightheadedness. This feeling may pass in a few seconds as the body
adapts. However, if dehydration or medications (for example, beta
blockers) prevent the body from reacting by constricting blood vessels and
increasing the heart rate, the dizziness may persist to the point at which the
patient passes out (faints, or experiences syncope).
Some diseases are associated with an inability to compensate for changes in
body position (autonomic dysfunction). Normally when a person stands, blood
vessels contract to increase blood pressure slightly, and the heart rate
increases to pump blood up to the brain against gravity. In autonomic
dysfunction, a person may become dizzy when they move from a lying position to
sitting or standing up.
Examples of these diseases include
Addison's disease, or
Orthostatic hypotension is a common symptom with
Shy-Drager syndrome is a rare disease in which the autonomic nervous system
degenerates and cannot provide the routine control mechanisms for the body
including heart rate, blood pressure, and bowel and bladder function.