Low blood pressure leads to fainting?

Dear Alice,

I have always had low blood pressure, which by all accounts is good. However, in the past year and a half, I have "fainted" three times when I was sick and I was told my low blood pressure might be the cause (I don't lose consciousness, but my body suddenly can't hold itself up and I fall with no control). The first two times, it was when I took a hot shower while sick and didn't leave a window open, the third time was when I had a bad bout of diarrhea w/fever and hadn't eaten in about 10 hours. The last spell was really bad, since I ended up crashing into the wall hard enough to leave bruises and hitting my head on a door before I fell. The fact that this "fainting" is a recent development worries me. Can low blood pressure be the cause? Should I be concerned, and what can I do to prevent it?

— This Flower is Wilting

Dear This Flower is Wilting,

The analogy in your signature, in addition to being sweet and endearing, is pretty accurate. A flower wilts when it doesn't get enough water and other nutrients, or when it's been left in excessive heat for too long. Your wilt could be caused by the same conditions. Since your fainting occurs in very specific circumstances, a combination of these factors may work together to exacerbate your low blood pressure.

In the hot shower your fainting could have been caused by a combination of heat, poor airflow, and being sick. Heat dilates veins and lets blood pool in the lower limbs, restricting its flow to the brain. When the brain is deprived of blood, and therefore oxygen, fainting can occur. Lack of proper ventilation is a well-known and common trigger for fainting, because of the lack of oxygen to the brain. Finally, because you were sick during these times you may have been dehydrated as well, which would exaggerate possible effects of low blood pressure by reducing the volume of the blood, which is largely water.

The third fainting incident could be attributed to dehydration and low blood sugar. Not eating for ten hours likely resulted in low blood sugar, which can deprive the brain of glucose causing dizziness and fainting. In addition, diarrhea is dehydrating, and as explained above, dehydration lowers blood pressure. In all three instances, many factors converged to make fainting more likely. While disconcerting and disorienting, fainting is actually a mechanism of rebalance for your body. When you fall and lie horizontally, more blood (and oxygen) flows to your brain.

You are absolutely correct that low blood pressure, also called hypotension, is usually a healthy trait. There are many conditions that could cause low blood pressure, some of them are in fact positive, like being cardiovascularly fit. But hypotension could also be the result of conditions that would require medical attention like a heart condition or diabetes. Visiting your health care provider may help to uncover the reason for your fainting, and determine if your low blood pressure is something you need to monitor.

Because you know you have low blood pressure naturally, making sure you're well hydrated and well fed is a good idea, especially when sick or before taking a hot shower. Although it feels good to step from a steamy shower into a warm bathroom cloudy with the scents of your favorite shampoo, it would be wise to leave a window open or fan on to ensure there's plenty of fresh air for you to breathe.

One of the most common causes of dizziness and fainting, especially for those with low blood pressure, is sudden change in posture. Have you noticed dizziness when you stand suddenly? If so, try rising slowly and gradually, giving the blood a chance to flow up from the lower body to the head. Similarly, when having blood drawn, see if the technician can do it with you lying down. Keeping a record of your symptoms, when they occur, and what you were doing at the time will also help you understand which situations to watch out for as potential triggers for fainting spells.

Finally, certain medications (including drugs used for anxiety, high blood pressure, nasal congestion, and allergies) can lead to fainting by causing a drop in your blood pressure. You may want to talk with your health care provider before taking these types of medications. Other reasons you may faint include hyperventilation, use of alcohol or drugs, or low blood sugar. Eliminating or lessening your exposure to these triggers could help to avoid dizziness or fainting.

With this information may you grow strong, sweet flower, and delight in an increasingly droop-free life.

Last updated Jun 25, 2015
Originally published Oct 19, 2007