What Happens When You Have A Sudden Drop in Blood Pressure?

dizzy woman holding head
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Low blood pressure, also known as hypotension, is a condition where your blood pressure is lower than what is considered normal for your age.

Most physicians consider "normal" blood pressure to be less than less than 120/80 mm Hg. Some people naturally have lower than average blood pressure, while others may have a medical condition that leads to lower-than-average blood pressure, or may be taking a medication that causes hypotension.

As long as your low blood pressure doesn't cause symptoms, most doctors believe it's okay.

However, a sudden drop in blood pressure that does cause major symptoms such as fainting, confusion, blurred vision or weakness likely indicates a medical emergency, such as an anaphylactic allergic reaction, a heart attack, dehydration or a serious infection or injury. If you experience these symptoms suddenly, you should seek medical help.

When blood pressure drops too far too quickly, blood stops circulating the way it should. This can lead to a life-threatening condition called shock.

Symptoms of Sudden Drops in Blood Pressure

What exactly happens when you experience a sudden drop in blood pressure? Here are some symptoms you may experience:

  • Dizziness
  • Blurred vision
  • Fainting
  • Nausea or vomoting
  • Pale, blue-tinged skin
  • Cold, clammy skin
  • Confusion
  • Breathing quickly
  • Unusual thirst
  • Sleepiness

You may have most of these symptoms, or just a few.

What Causes Sudden Low Blood Pressure?

As I said above, sudden low blood pressure can result from an anaphylactic allergic reaction, a reaction to a medication you're taking, from a serious injury or infection, or even from a heart attack.

In anaphylaxis, for example, the drop in blood pressure occurs because your body releases large amounts of chemicals, including histamine, in response to the presence of an allergen (this allergen can be a food you ate or the venom from an insect bite).

The chemicals your body releases cause your blood vessels to dilate, or get wider, which then in turn causes your blood pressure to suddenly plummet.

Other symptoms of an anaphylactic reaction include difficulty breathing coupled with a feeling that your throat is closing, skin redness and hives, and cramps (possibly with diarrhea).

This type of allergic reaction is a medical emergency. Treatment most likely will start with an injection of epinephrine, which will raise your blood pressure and halt the allergic reaction that's threatening your breathing. Your medical team may also administer antihistamines and other treatments, as necessary.

Other causes of sudden low blood pressure also are serious medical problems. When in doubt and if experiencing symptoms, you should seek medical assistance.


American Heart Association. Low Blood Pressure fact sheet. Accessed Nov. 6, 2015.

NIAID-Sponsored Expert Panel. Guidelines for the Diagnosis and Management of Food Allergy in the United States: Report of the NIAID-Sponsored Expert Panel. The Journal of Allergy and Clinical Immunology. Volume 126, Issue 6, Supplement , Pages S1-S58, December 2010.

Sampson HA et al. Second symposium on the definition and management of anaphylaxis: Summary report—Second National Institute of Allergy and Infectious Disease/Food Allergy and Anaphylaxis Network symposium. The Journal of Allergy and Clinical Immunology. February 2006. Volume 117, Issue 2, Pages 391–397.

U.S. National Library of Medicine. Drop in Low Blood Pressure fact sheet. Accessed Nov. 6, 2015.

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