Orthostatic hypotension — also called postural hypotension — is a form of low blood pressure that happens when you stand up from sitting or lying down. Orthostatic hypotension can make you feel dizzy or lightheaded, and maybe even faint.
Orthostatic hypotension may be mild and last for less than a few minutes. However, long-lasting orthostatic hypotension can signal more-serious problems, so it's important to see a doctor if you frequently feel lightheaded when standing up.
Occasional (acute) orthostatic hypotension is usually caused by something obvious, such as dehydration or lengthy bed rest, and is easily treated. Chronic orthostatic hypotension is usually a sign of another health problem, so treatment varies.