A sudden drop in blood pressure upon standing is termed:

A sudden drop in blood pressure upon standing is referred to as orthostatic hypotension. This condition occurs when the body struggles to properly regulate blood pressure during changes in posture, particularly from lying down or sitting to standing. When a person stands up, gravity causes blood to flow to the lower parts of the body, and if the compensatory mechanisms fail to maintain adequate blood flow to the brain, it can result in a temporary drop in blood pressure. Symptoms can include dizziness, lightheadedness, or even fainting.

The other conditions listed do not specifically pertain to the phenomenon of blood pressure fluctuation related to posture changes. Septic shock is a severe and systemic response to infection, characterized by low blood pressure due to widespread inflammation and organ failure. Postprandial hypotension involves a drop in blood pressure following a meal, which is unrelated to changes in body position. Hypovolemic shock refers to a state of shock resulting from significant blood or fluid loss, affecting overall blood volume rather than postural changes. Thus, orthostatic hypotension is the condition specifically associated with the abrupt drop in blood pressure experienced when standing.