A sudden drop in blood pressure can be caused by a rapid change in health or certain medications. It may also signify an underlying medical problem such as thyroid issues. As long as there are no symptoms, low blood pressure in an otherwise healthy person generally is not a concern.
There are certain situations, however, in which a blood pressure decline may cause problems or be indicative of a health issue that should be addressed by a doctor. Current guidelines typically classify normal blood pressure as between 90/60 mm Hg and 120/80 mm Hg. While high blood pressure is very common, it is possible to have blood pressure that is too low as well.
"A single lower-than-normal reading is not cause for alarm if you are not experiencing any other symptoms or problems. However, a sudden drop in blood pressure – even a change of just 20 mm Hg – can cause dizziness or fainting," according to the American Heart Association. Sit down if you feel dizzy and drink water, because dehydration can cause a drop in blood pressure.
Blood Pressure Varies Between People
Blood pressure is a measurement of the pressure within your arteries while your heart is contracting (systolic pressure) and relaxing (diastolic pressure). Your blood pressure is expressed as the systolic (top) value being first and the diastolic (bottom) value second. Some experts define low blood pressure — called hypotension — as a measurement of either less than 90 systolic or less than 60 diastolic. But what is a normal blood pressure for you depends on many factors, including genetics. Regular exercise helps to lower blood pressure and people who eat a healthy diet, maintain a healthy weight and do not smoke tend to have lower blood pressure as well.
What Is Orthostatic Hypotension?
A sudden drop in blood pressure of 20 mm Hg or more can be dangerous, causing dizziness and sometimes fainting because the brain is not receiving adequate amounts of blood. A change in body position, for instance going from sitting or lying down to standing upright, which can cause an extreme drop in blood pressure, is called postural or orthostatic hypotension. Dehydration can contribute to orthostatic hypotension and is common after eating, which is called postprandial hypotension, as blood is drawn to the digestive tract and away from other areas. Older adults tend to be more susceptible to orthostatic hypotension.
Rapid Changes in Health Can Cause an Acute Drop in Blood Pressure
Certain medical conditions can cause an acute drop in blood pressure. Blood loss from either an external injury or internal bleeding, for instance, will cause a drop in blood pressure. Excessive blood loss during menstruation could also be a cause. Dehydration – from fever, vomiting and diarrhea, for example – can also cause hypotension. Severe infection (septic shock) or a severe allergic reaction (anaphylactic shock) can result in hypotension. Blood pressure will also drop with heart failure as the damaged heart cannot pump the blood adequately.
Read more: Why Does Blood Pressure Drop After a Meal?
Medications Can Contribute to Sudden Drops in Blood Pressure
There are several medications that will directly cause drops in blood pressure or make you more susceptible to sudden hypotension. Obviously medications used to treat high blood pressure work to relax the blood vessels and reduce pressure. These include beta blockers, ACE inhibitors, calcium channel blockers and nitrates.
Diuretics will lower blood pressure, too, by reducing the amount of fluid in the body. Some antidepressants, anti-anxiety medications, drugs for Parkinson’s disease and drugs for erectile dysfunction can also cause drops in blood pressure. Check with your doctor to find out if any of the medications you are currently taking could be causing low blood pressure.
Drops in Blood Pressure May Indicate Underlying Medical Problems
Hypotension can also be a symptom of several medical conditions, such as an underlying endocrine problem like thyroid or parathyroid issues. It could also indicate a problem with the heart, such as a valve problem or damaged heart muscle. Sometimes hypotension can indicate a neurological condition where there is miscommunication between the brain and the heart.
While it’s not necessarily a rapid change, or a medical problem for that matter, you should be aware that blood pressure typically drops during pregnancy as the woman’s circulatory rapidly expands.
When to See a Doctor About Sudden Low Blood Pressure
Symptoms of low blood pressure may include, according to the AHA, dizziness or lightheadedness; fainting; dehydration and unusual thirst; lack of concentration; blurred vision; nausea; cold, clammy, pale skin; rapid, shallow breathing; fatigue and depression. "If you experience any dizziness or lightheadedness, it's a good idea to consult with your healthcare provider," recommends the AHA.