Final answer:
Orthostatic hypotension is characterized by a sudden drop in blood pressure upon standing, causing dizziness due to decreased blood flow to the brain. It can be caused by low blood volume or autonomic failure.
Step-by-step explanation:
The term that refers to a sudden, dramatic drop in blood pressure (BP) upon standing or sitting up straight is orthostatic hypotension. This condition occurs when the cardiovascular system cannot adjust quickly enough when changing position from sitting or lying down to standing, leading to a temporary decrease in blood flow to the brain and a feeling of dizziness or light-headedness. Two main causes of orthostatic hypotension are low blood volume, often due to dehydration or certain medications like diuretics or vasodilators, and autonomic failure, as seen in disorders such as diabetes and multiple system atrophy.