Orthostatic hypotension is defined as:

Orthostatic hypotension is characterized by a significant drop in blood pressure when an individual transitions from a sitting or lying position to a standing position. This drop in blood pressure can lead to symptoms such as dizziness, lightheadedness, or even fainting, particularly when standing up quickly.

The condition arises due to the body's inability to properly adjust blood flow and vascular resistance upon changing positions, a response that is normally regulated by the autonomic nervous system. When standing, gravitational forces can temporarily pool blood in the lower extremities, and in a healthy individual, compensatory mechanisms should kick in to maintain cerebral perfusion and prevent significant drops in blood pressure.

In contrast, the other options do not accurately reflect the phenomenon associated with orthostatic hypotension. For instance, a rise in blood pressure upon standing would suggest an appropriate autonomic response, while stable blood pressure in all positions would indicate normal physiological function. An increase in heart rate with standing can occur in some cases as a compensatory mechanism, but it is not the defining characteristic of orthostatic hypotension itself.