JH is a 67-year-old male who presents to the clinic with complaints of dizziness and lightheadedness upon standing. His blood pressure is 140/80 mmHg while sitting but drops to 115/70 mmHg upon standing His past medical history includes type 2 diabetes, hypertension, myocardial infarction (heart attack) at age 63, arthritis, two falls in the past year, and hyperlipidemia. His current medications include: Lantus 50 units at bedtime, amlodipine 5 mg daily, metoprolol succinate 50 mg daily, atorvastatin 40 mg nightly, and aspirin 81 mg daily. He reports starting vitamin D3 5,000 unit capsules two weeks ago based on his wife's recommendation. His symptoms are consistent with