Have you ever gotten up too quickly from your chair and suddenly feel light-headed? That dreaded feeling where you’re disoriented and lose your sense of balance has happened to nearly everyone before, and there’s a good explanation for it.

According to an article in Time magazine, scientists have called this occurrence initial orthostatic hypotension (OH), and this usually happens when your blood circulation is affected.

“These symptoms occur because there is a temporary decrease in the amount of blood—and therefore oxygen—supplied towards the brain,” says Dr. M.A. Ikram, an OH researcher and chair of epidemiology at Erasmus University Medical Center Rotterdam in the Netherlands.”

This is due to gravity having an effect on the way blood circulates while you’re sitting down. Once you’ve been in that position for awhile, your heart needs to work a little harder to get up to your brain.

“The heart is a pump, and when you stand up suddenly, the amount of blood going into the heart is reduced,” says Dr. Phillip Low, a professor of neurology at Mayo Clinic in Rochester, Minn., who performed research investigating the causes and symptoms of OH. “This can cause a temporary drop in blood pressure, and it takes a short amount of time for the corrective mechanisms to kick in and correct it.”

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So is it something you should be worried about?

Most of the time, the answer is no. OH is usually not harmful if symptoms go away after a few seconds. However, it may be an indication of something more severe especially if you’re above the age of 40. The best thing to do if you feel its affects for a prolonged period is to see your doctor as soon as you can to get it checked out.

By Gilbert Wong, Men’s Health Content Producer

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