What Happens When You Have A Sudden Drop in Blood Pressure

Potential causes include medications, allergic reactions and infection

woman having blood pressure taken

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

Some people naturally have lower than average blood pressure, which generally is considered to be beneficial, since high blood pressure is a significant risk factor for serious health conditions such as heart disease and stroke.

Other people may have a medical condition that can lead to lower-than-average blood pressure, such as Addison's disease, or may be taking a medication that causes hypotension, such as certain drugs used to treat Parkinson's disease.

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

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 vomiting
  • Pale, blue-tinged skin
  • Cold, clammy skin
  • Confusion
  • Breathing quickly
  • Unusual thirst
  • Sleepiness

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

Causes

As mentioned 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.

Diagnosis

Once your blood pressure has been stabilized, your doctor will look for the reason you experienced this drop in blood pressure. Some causes may be obvious; for example, if you have known food allergies and were exposed to the allergen, you may have had an allergic reaction that caused your hypotension. Other potential causes may take some sleuthing to uncover.

If your symptoms are sudden and serious, such as a fainting spell or confusion, your doctor may recommend additional tests. Some serious conditions, including blood loss from internal bleeding, a severe infection, and anemia, can cause low blood pressure. Pregnancy also can cause low blood pressure.

Your treatment for your low blood pressure will depend on the cause. A severe infection, for example, likely will require antibiotics. Anemia can have many different causes, including poor diet, certain chronic diseases, and cancer.

A Word from Verywell

If you only experience occasional symptoms related to your low blood pressure, such as lightheadedness, it's likely you'll only need routine medical monitoring for the condition. Your doctor may advise you to purchase a home blood pressure machine to track your blood pressure.

However, if you experience repeated symptoms of sudden low blood pressure, even if they seem relatively minor, talk to your doctor about it. It may be that something simple, such as an adjustment of your medications, could fix the problem.

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Article Sources
  • American Heart Association. Low Blood Pressure fact sheet.
  • 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.