Why Does Standing Up Sometimes Make You Dizzy?

By Howard J. Bennett

Has this ever happened to you? You’re lying in bed on a Saturday morning thinking about how great it is that you don’t have to get up for school. After snuggling with your blanket for a while, your slumber is interrupted by annoying signals from your bladder that you have to pee. However, when you stand up to go to the bathroom, you feel really dizzy and have to sit down.

What you just experienced was a temporary drop in blood pressure that occurred because your blood “pooled” in your legs as you stood up. Once your brain realized it wasn’t getting all the blood (and oxygen) it needed, you felt dizzy and sat down as a protective mechanism to prevent you from fainting—and bonking your head on the floor. While this was happening, your nervous system made rapid adjustments to increase your blood pressure so you could get to the bathroom and make your bladder happy.

Your body’s nervous system is broadly divided into two parts. The system that gets the most attention is the conscious part. This is the part that allows you to think, plan and manipulate your environment. It is your conscious brain that allows you to do you homework or procrastinate about it.

Your body also has something called the autonomic (au-to-NA-mic) nervous system. This is the part that takes care of things that don’t ever think about such as heart rate, digestion, perspiration, and yes, peeing. Some parts of the nervous system such as breathing can be under conscious and unconscious control.

As far as the circulatory system goes, your autonomic nervous system is constantly monitoring how much blood pressure is needed to keep everything moving efficiently. If you ever felt your heart pounding after you got dizzy, it was caused by adrenaline that was released into the bloodstream increase your blood pressure.

When you are lying down, it is easier for your heart to pump blood through your body because it doesn’t have to work against gravity. As a result, your blood pressure drops a bit. When you stand up, things change rapidly. The autonomic nervous system sends out signals telling the arteries in your arms and legs to constrict (tighten) so blood can get back to the heart and be pumped to your brain and the rest of your body. A delay in this response causes dizziness.

There are a few situations that increase your chances of getting dizzy when you stand up.

• Being sick.

• Not having enough to drink and getting dehydrated, especially on a hot day.

• Not eating breakfast.

• Standing up for a long time.

If you ever feel dizzy, SIT DOWN right away until the feeling passes. If you don’t, you may faint and gravity will make sure you sit down, sometimes with embarrassing results.

© 2012 Howard J. Bennett. All Rights Reserved.
(First published in the Washington Post 6/14/10.)

For more KidsPost articles and lots of other cool stuff,
please visit Dr. B’s website at  www.howardjbennett.com.

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