Postural hypotension (or orthostatic hypotension) is when your blood pressure drops when you change position from lying down to sitting or standing, or from sitting to standing. It is common in older people. When your blood pressure drops, less blood goes to your organs (including your brain) and muscles. This can make you lightheaded, dizzy, nauseous and weak and, in more severe cases faint. This is how postural hypotension increases your risk of falling.