**Core Concept:** Postural hypotension refers to a decrease in blood pressure upon standing or changing position, particularly in the supine position. It is a common problem in geriatric patients and can be caused by age-related factors, medication side effects, or neurological disorders.

**Why the Correct Answer is Right:** Postural hypotension is primarily caused by the autonomic nervous system's dysfunction in modulating blood pressure. When standing up, the body needs to increase blood pressure to maintain cerebral perfusion. This is achieved by the sympathetic nervous system's release of norepinephrine into the vasculature, which constricts blood vessels and increases heart rate. In a healthy individual, this reflex is strong enough to counteract the decrease in blood volume due to the legs moving away from the heart.

In this scenario, option D is correct because postural hypotension is not seen in individuals with a strong autonomic nervous system's response to standing, as the sympathetic nervous system can maintain adequate blood pressure despite the body's position change.

**Why Each Wrong Option is Incorrect:**

A. Postural hypotension may occur in patients with intact autonomic function, indicating that the issue is not solely about autonomic function.

B. Although postural hypotension can be seen in patients with orthostatic hypotension, it is not exclusively limited to this condition.

C. Postural hypotension can occur in patients with a strong sympathetic response to standing, disproving the assumption that it is seen in patients with weak sympathetic response.

**Clinical Pearl:** Postural hypotension is a symptom that may hint at an underlying cause. In the elderly, it is a common feature of autonomic neuropathy, a group of disorders affecting the autonomic nervous system. Assessing for risk factors such as medication use, dehydration, and orthostatic hypotension can help guide further evaluation and management of this condition.