Why do you get dizzy when standing up?

Dizziness upon standing up may be caused by an abnormal drop in blood pressure, states Merck Manual. This abnormal drop in blood pressure is often referred to as orthostatic hypotension.

Orthostatic hypotension most often affects older individuals, states Merck Manuals. Symptoms of this condition including faintness, dizziness, confusion and blurred vision directly after standing up. Younger individuals who experience dizziness upon standing may be experiencing orthostatic hypotension, but they may also be experiencing an increased heart rate. If the latter is true, then they may have a medical condition known as postural orthostatic tachycardia syndrome. This syndrome is more common in younger patients than older patients.