What is considered a dangerously low blood pressure reading?

Updated February 21, 2017

Hypotension means low blood pressure, while hypertension means high blood pressure. If you think you are experiencing problems due to low blood pressure, such as dizziness, it's important to see your doctor, as you may have an underlying medical condition. If you are on any medications, check with your doctor to see if it may cause changes in blood pressure.


According to the American Heart Association, having low blood pressure is relative to your own normal blood pressure. That is, rather than a specific number at which blood pressure is too low, having a sudden drop in your normal blood pressure is considered dangerous. A drop of 20 mmHg or more can cause severe reactions (see Resources).


Symptoms of a sudden drop in blood pressure include dizziness, fainting, fatigue, nausea, blurred vision and hyperventilation.


Causes for a sudden drop in blood pressure may be quite serious, and include a heart or neurological problem, severe allergic reaction or a serious infection. It can also be caused from excessive blood loss and dehydration.

Normal Values

An average blood pressure reading is about 112/64 mmHg. A blood pressure reading below 120/80 mmHg is safe.


In some cases, blood pressure readings are inaccurate due to anxiety and stress a patient may feel from being examined by a doctor. Stress can cause blood pressure to rise.

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About the Author

Catherine Chase is a professional writer specializing in history and health topics. Chase also covers finance, home improvement and gardening topics. She holds a Bachelor of Arts in American studies from Skidmore College.