Postural = Having to do with
posture.
Hypo- = a
deficiency, and
tension = stretching.
Also called orthostatic hypotension.
Postural hypotension is the medical name for the dizziness and light-headedness that you get from standing up too fast. It's caused by the delay while your heart and blood vessels adjust to your new position, during which there is a shortage of oxygen to the brain. Once the heart speeds up and the blood vessels constrict and contract, things should return to normal.
Normally this isn't a problem, but if it happens excessively, doesn't fade quickly, or causes fainting, you should see a doctor.
Possible causes of postural hypotension are:
Dehydration
Diabetes
Blood loss, possibly unnoticed gastrointestinal bleeding
Spinal injuries
Medications, such as antihypertensives, diuretics, and beta-blockers