Why do you sometimes get dizzy when you stand up?

By Howard Bennett
Monday, June 14, 2010

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. When you stand up to go to the bathroom, you feel 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 to prevent yourself from fainting. 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 nervous system is broadly divided into two parts. The system that gets the most attention is the conscious part. This allows you to think, plan and manipulate your environment. It is your conscious brain that allows you to do your homework or procrastinate about it.

Your body also has something called the autonomic (pronounced au-to-NO-mic) nervous system. This is the part that takes care of things that you don't ever think about, such as heart rate, digestion and perspiration. Some parts of the nervous system, such as breathing, can be under conscious or unconscious control.

As far as the circulatory system goes, your autonomic nervous system monitors how much blood pressure is needed to keep things moving. If you ever felt your heart pounding after you got dizzy, it was because adrenaline increased your blood pressure.

When you lie 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 causes dizziness.

Here are a few situations that increase your chances of getting dizzy when you stand up: -- Being sick.

-- Not having had enough to drink and getting dehydrated.

-- Not eating breakfast. -- Standing up for a long time.

If you ever feel dizzy, SIT DOWN right away until the feeling passes.

-- Howard Bennett

Howard Bennett, a Washington pediatrician and author of health-related books for kids, writes about gross things for KidsPost.

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