Top Reasons for Passing Out: Causes and Prevention Explained

Passing out (syncope) can be caused by dehydration, standing up fast, low blood pressure, heart rhythm problems, or stress. Get medical care after fainting.

What it is

Passing out (syncope) is a temporary loss of consciousness from reduced blood flow to the brain. About a third of people faint at some point.

Common causes

• Vasovagal reaction: stress, pain, blood sight, heat.
• Orthostatic hypotension (standing up quickly).
• Dehydration or not eating.
• Heart rhythm problems or heart disease.
• Medications.

What to do

Lie down and raise the legs. Check breathing.

Call 911 if

The person doesn’t wake in a minute, is injured, has chest pain, has an irregular heartbeat, is pregnant or has a seizure.

See a doctor

Anyone who faints with no clear cause or during exercise should get a heart check.

Prevention

Drink water, rise slowly, and avoid triggers.

What passing out is

Passing out, or syncope, is a brief loss of consciousness caused by a temporary drop in blood flow to the brain. People recover on their own within seconds to minutes. Syncope accounts for about 1% to 3% of emergency visits in the US, and about one third of people faint at least once in their life.

Common causes

• Vasovagal syncope, the most common, triggered by pain, the sight of blood, stress, standing for long periods or heat.
• Orthostatic hypotension, a drop in blood pressure on standing, caused by dehydration, blood loss, some medicines or age.
• Heart rhythm problems such as bradycardia, tachycardia or long QT syndrome.
• Structural heart disease, such as aortic stenosis.
• Low blood sugar in diabetics.
• Situational triggers: coughing, urination or straining.
• Dehydration and heat exhaustion.

Warning signs

Many people feel lightheaded, nauseated, sweaty, pale, warm or notice tunnel vision and ringing in the ears before they pass out. If this happens, lie down or sit with the head between the knees. Crossing the legs and tensing the muscles can raise blood pressure.

What to do when someone faints

• Lay the person flat and raise the legs about 12 inches above the heart.
• Loosen tight clothing and make sure the airway is clear.
• Check breathing. If the person is not breathing, start CPR and call emergency services.
• Do not give food or drink until alert.
• Have them sit up slowly after recovering.

Call 911 if

The person does not wake within a minute, has chest pain, a racing or irregular heartbeat, shortness of breath, injuries from falling, seizure like activity, is pregnant, or has diabetes. Fainting during exercise is a red flag for heart disease.

Diagnosis

Doctors check blood pressure sitting and standing, ECG, blood tests, and may use heart monitors, echocardiogram, or a tilt table test. Fainting with no warning, family history of sudden death or heart disease needs a full cardiac evaluation.

Prevention

Drink fluids (around 2 liters a day unless restricted), add salt if advised by a doctor, avoid triggers, rise slowly from lying or sitting, and review medicines with a doctor.

Types of fainting in numbers

Syncope accounts for about 1 to 3 percent of emergency department visits in the US. Vasovagal syncope is the most common type, followed by orthostatic hypotension and cardiac causes. Cardiac syncope has the highest risk of death and is more common in older adults and people with heart disease. A person who faints usually recovers consciousness within a minute. After fainting, avoid standing up quickly, and lie flat for 10 to 15 minutes. People who faint during exercise, with palpitations or with a family history of sudden death should see a doctor for an ECG and further testing.

Based on data from the American Heart Association and the American College of Cardiology