Low blood pressure (hypotension) is a condition in which the force of blood pumping through the arteries is lower than normal.
However, there is no specific measurement at which blood pressure is considered too low, and it is generally not a reason for concern as long as a person has no troublesome symptoms.
For some people, a low blood pressure is normal, and for the most part, the lower the blood pressure reading, the better.
Blood pressure is expressed in two numbers:
- Systolic blood pressure (the first/top number): measures the pressure in the blood vessels when the heart beats
- Diastolic blood pressure (the second/bottom number): measures the pressure in the blood vessels when the heart is at rest between beats
Low, normal, elevated, and high blood pressure is usually defined in the following ranges:
- Low blood pressure is 90/60 mm Hg
- Normal blood pressure is less than 120/80 mmHg
- Elevated blood pressure levels between 120/80 and 139/89 are considered prehypertension and mean a person is at higher risk for developing high blood pressure
- High blood pressure (hypertension) is 140/90 mmHg or more
Reasons a person’s blood pressure might be low include:
- Prolonged bed rest
- Pregnancy, especially during the first 24 weeks when it’s common for blood pressure to drop
- Decreases in blood volume, such as from major trauma, dehydration, or severe internal bleeding or anemia
- Certain medications, including diuretics, other drugs that treat high blood pressure (hypertension), heart medications such as beta blockers, drugs for Parkinson's disease, tricyclic antidepressants, erectile dysfunction drugs (especially in combination with nitroglycerine), narcotics, and alcohol
- Heart problems, such as abnormally low heart rate, heart valve problems, heart attack, and heart failure
- Endocrine problems, such as underactive thyroid (hypothyroidism), parathyroid disease, adrenal insufficiency (Addison’s disease), low blood sugar and diabetes
- Problems with the autonomic nervous system, such as Parkinson’s disease
- Severe infection (septic shock)
- Severe allergic reaction (anaphylaxis)
- Neurally mediated hypotension, a disorder that causes blood pressure to drop after standing for long periods
- Nutritional deficiencies, including a lack of vitamins B-12 and folic acid
- Older age
What Are Symptoms of Low Blood Pressure?
Chronically low blood pressure is usually only considered a medical concern if it causes noticeable symptoms such as:
- Dizziness
- Lightheadedness
- Nausea
- Fainting
- Dehydration
- Unusual thirst
- Inability to concentrate
- Blurred vision
- Cold, clammy, pale skin
- Fatigue
- Depression
Extremely low blood pressure prevents the body’s vital organs from getting the oxygen and nutrients they need. If this occurs, low blood pressure can lead to shock, which is a medical emergency. Call 911 and get to a hospital’s emergency department (do not drive yourself) if you notice signs of shock including:
- Cold and sweaty skin
- Rapid, shallow breathing
- Blue skin tone
- Weak and rapid pulse
What Is the Treatment for Low Blood Pressure?
Low blood pressure may not require treatment if it causes no symptoms. When symptoms do occur, treatment depends on the specific signs and symptoms, and may include:
- Drinking more fluids
- Medication to raise blood pressure
- Adjusting medicines that cause low blood pressure (never change the dose or regimen of a prescribed medication without first talking to your doctor)
- Lifestyle changes
- Changing what and how you eat
- Changing how you sit and stand up
- Compression stockings
From 
Heart Health Resources
https://www.nhlbi.nih.gov/health-topics/low-blood-pressure