Q: When I stand up, things often go dark briefly. I've always had this, but now a friend says it could be something bad. Should I worry?

–Joanne First, 73, Fair Lawn, NJ

A: The medical term for what you're experiencing is presyncope—which is when you feel like you're about to pass out. (If you actually do faint, we call that syncope.) Your friend is right—you should discuss it with your doctor, because presyncope can signal a serious condition, such as low red blood cell counts or even a heart problem.

The good news, however, is that it likely isn't something serious. The most common explanation for pre-syncope (in otherwise healthy people) is something we call postural hypotension-a temporary drop in blood pressure that may occur when you get up after you've been sitting or lying down for a while. You'll be glad to know that most often, it's benign.

Postural hypotension typically happens when you've been seated or horizontal long enough for blood to pool in your legs. When you stand up, it takes your body a few seconds to adjust to the change in position and send enough blood and oxygen to your brain. It's that lack of oxygen that makes you feel light-headed or dizzy. You're more prone to the condition if you have low blood pressure at baseline or if you usually get heavy periods (in which case you might want to ask your doc if you'd benefit from taking an iron supplement).

More from Prevention: Dr. Stork's Lean Belly Tips

Although postural hypotension is often not a sign of anything serious, it can be dangerous in its own right, simply because you can fall and hurt yourself when it happens. I've seen plenty of people come into the emergency room with head injuries from an accident caused by a fainting or near-fainting spell.

So if this is an issue for you, it's good to be aware of it. Get in the habit of taking a few extra seconds to stand up after you've been sitting for a while. And because dehydration can exacerbate these episodes, make sure you drink plenty of fluids, and be careful in hot weather or when using a sauna.

TRAVIS STORK, MD, is an ER physician, cohost of TV's The Doctors, and the author of The Lean Belly Prescription.

Send your questions for Dr. Stork to askdrstork@prevention.com.

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