**Core Concept**
Orthostatic hypotension is a sudden drop in blood pressure upon standing, leading to dizziness and potential syncope. It's a common issue in patients with autonomic nervous system dysfunction, dehydration, or taking medications that cause vasodilation.

**Why the Correct Answer is Right**
The treatment of orthostatic hypotension involves increasing blood volume, improving blood pressure regulation, and enhancing vasomotor tone. Fludrocortisone, a synthetic corticosteroid, helps by increasing blood volume and promoting sodium retention. Midodrine, a selective alpha-1 adrenergic receptor agonist, directly increases peripheral vascular resistance, thereby raising blood pressure.

**Why Each Wrong Option is Incorrect**
**Option A:** Volume expansion with IV fluids may provide temporary relief but doesn't address the underlying autonomic dysfunction or vasomotor tone issues.
**Option B:** Flunarizine, a calcium channel blocker, would actually worsen orthostatic hypotension by further reducing peripheral vascular resistance.
**Option C:** Beta blockers can decrease blood pressure and heart rate, exacerbating orthostatic hypotension.

**Clinical Pearl / High-Yield Fact**
To manage orthostatic hypotension effectively, consider using a combination of fludrocortisone and midodrine, and advise patients to rise slowly from a seated or lying position to minimize initial blood pressure drops.

**Correct Answer: D. Midodrine**