When the blood pressure is too low, there is inadequate blood flow to the heart, brain, and other vital organs.

A blood pressure level that is borderline low for one person may be normal for another. The most important factor is how the blood pressure changes from the normal condition. Most normal blood pressures fall in the range of 90/60 mm Hg to 130/80 mm Hg, but a significant change, even as little as 20 mm Hg, can cause problems for some people.

Low blood pressure is commonly caused by drugs such as the following

• Medications used for surgery
• Anti-anxiety agents
• Treatment for high blood pressure
• Diuretics
• Heart medicines
• Some antidepressants
• Narcotic analgesics
• Alcohol

Other causes of low blood pressure include the following:

• Dehydration
• Heart failure
• Heart attack
• Changes in heart rhythm (arrhythmias)
• Fainting
• Anaphylaxis (a life-threatening allergic response)
• Shock (from severe infection, stroke, anaphylaxis, major trauma, or heart attack)
• Advanced diabetes

Another common cause type of low blood pressure is orthostatic hypotension, which results from a sudden change in body position, usually from lying down to an upright position.

Call your local emergency number (such as 911) if someone is unconscious. If trained in basic life support (BLS) or advanced cardiac life support (ACLS), check the person's ABCs (airway, breathing, and circulation). If the person is NOT breathing or has NO pulse, begin CPR.

Call your doctor immediately if you:

• Feel dizzy, lightheaded, or faint
• Have black or maroon stools
• Have chest pain, shortness of breath, an irregular heartbeat, fever higher than 101 degrees, headache, stiff neck, or severe upper back pain

Also call your doctor if you have:

• Cough with phlegm
• Prolonged diarrhea or vomiting
• Inability to eat or drink
• Burning with urination or other urinary symptoms
• You are taking any new medications

In emergencies, the seriousness of the condition will be determined first. Then, the health care provider will obtain your medical history and will perform a physical examination.

Frequent monitoring of vital signs (temperature, pulse, rate of breathing, blood pressure) and/or hospitalization may be necessary.

Medical history questions documenting low blood pressure may include the following:

• What is your normal blood pressure?
• What medications do you take?
• Have you been eating and drinking normally?
• Have you have any recent illness, accident, or injury?
• What other symptoms are also present?
• Did you faint or become less alert?
• Do you feel dizzy or light-headed when standing or sitting after lying down?

• Blood studies (such as CBC, blood differential)
• Cultures
• ECG
• Urinalysis
• X-ray of the abdomen
• X-ray of the chest