What are the causes of sudden drop in blood pressure?

Updated November 21, 2016

Low blood pressure in and of itself isn't anything to get worked up over unless you are symptomatic; however, if your blood pressure drops suddenly and drastically, that is a cause for concern. When your blood pressure is low, this can cause fainting or dizziness. If it's severely low, this can indicate serious problems such as endocrine or neurological disorders or heart disease. Severely and suddenly low blood pressure can deprive the body's organs and brain of nutrients and oxygen, which can lead to shock.

Relatively Speaking

The American Heart Association explains that low blood pressure is a relative term. What is low for you might not be for someone else who has always had low blood pressure. If you have chronically low blood pressure all the time, this is only considered a concern if it causes you problems such as fatigue and lightheadedness. A sudden drop, however, can be dangerous. A drop of just 20 mm Hg may result in dizziness or even fainting. Rapid drops can be indicative of an allergic reaction, severe infection or uncontrolled bleeding.


Severe dehydration can occur when you are sick and have diarrhoea or vomiting, or if you are overly exercising and/or using diuretics (water pills). This can result in a drastic and sudden drop in blood pressure. If you lose only 1 to 2 per cent of your body weight due to mild dehydration, this can result in symptoms such as fatigue and weakness.


Older people can experience a condition called postprandial hypotension, which means that their blood pressure drops suddenly after a meal. Usually these individuals have autonomic nervous system diseases, such as Parkinson's, or high blood pressure.

Change in Position

If you are one of those people who gets dizzy upon getting up from a sitting or prone position, you have what is called postural (orthostatic) hypotension, according to the Alberta Caregiver College. It causes blurred vision, lightheadedness, dizziness and sometimes fainting. This can be the result of taking certain medications such as antidepressants and anti-psychotics, beta blockers, calcium channel blockers, ACE inhibitors and medicines for Parkinson's disease. If you have been lying down too long and suddenly get up, this can cause postural hypotension, as can heart problems, the heat and diabetes.


If you are stung by a bee and experience anaphylactic shock, which is an extremely serious allergic reaction, this can cause a dramatic drop in blood pressure. Anaphylaxis can be fatal. Along with a severe drop in blood pressure, your throat can swell shut, and you won't be able to breathe.

Rapid Blood Loss

A rapid loss of blood, from an injury or even a heavy menstrual period, can lead to a drastic and sudden drop in blood pressure.

Get Treatment

If you are experiencing symptoms of low blood pressure, consult with your physician. She can determine if you have low blood sugar or are dehydrated or have other physical problems that are causing this. How quickly your blood pressure is dropping is of more importance than how low it drops.

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About the Author

Cindi Pearce is a graduate of Ohio University, where she received her bachelor’s degree in journalism. She completed both the undergraduate and graduate courses offered by the Institute of Children’s Literature. Pearce has been writing professionally for over 30 years.