Standing up suddenly can precipitate an unsteady moment as the body struggles to ratchet up blood pressure in response to the posture change. In some people, particularly those with Parkinson's disease, a stronger woozy feeling indicates a transient low-blood-pressure condition, called orthostatic hypotension, which can lead to falls.
While the muscle rigidity and tremors of Parkinson's disease result from cell death in parts of the brain that produce the neurotransmitter dopamine, the cause of orthostatic hypotension is less clear. Recently, scientists have found evidence suggesting that nerve endings in the hearts of Parkinson's patients can be damaged. A new study now directly links such cardiac-nerve dysfunction with orthostatic hypotension.