Fainting (Syncope): Causes and What to Do

What to do when someone faints

1. Lay the person flat on their back and raise their legs about 12 inches (30 cm) if possible. This helps blood return to the brain.
2. Check breathing. If they are not breathing normally, call 911 or your local emergency number and start CPR.
3. Loosen tight clothing around the neck and waist.
4. Do not sit them up quickly. Let them lie for 10 to 15 minutes, then sit up slowly.
5. If they vomit, roll them onto their side.
6. Call 911 if they do not wake within a minute, were injured, have chest pain or trouble breathing, or fainted during exercise.

If you feel a faint coming on, lie down or sit with your head between your knees. Physical counter-maneuvers can stop a reflex faint: cross your legs and squeeze your thighs and buttocks, or grip your hands together and pull your arms apart, for up to 30 seconds.

What happens during a faint

Before fainting, most people have warning signs (a prodrome) lasting seconds to minutes:

• light-headedness and feeling hot or clammy
• nausea and yawning
• tunnel vision, blurred or graying vision
• muffled hearing or ringing in the ears
• going pale

During the faint the person goes limp and falls. A few brief jerks of the arms or legs are common and do not mean a seizure. They usually come round within 20 to 30 seconds, and are alert straight away, though often tired, pale and sweaty for a while.

Causes of fainting

Reflex syncope (most common)

Vasovagal syncope is caused by an overactive reflex that suddenly slows the heart and widens blood vessels, so blood pressure falls. Triggers include:

• standing for a long time, especially in heat or crowds
• the sight of blood, needles or medical procedures
• pain, fear or emotional shock
• dehydration, skipping meals, or alcohol

Situational syncope follows specific actions: urinating (especially men at night), coughing fits, straining on the toilet, swallowing or laughing. Carotid sinus syncope happens in older people when pressure on the neck, from turning the head or a tight collar, triggers the reflex.

Orthostatic hypotension

Orthostatic hypotension is a fall in blood pressure on standing up. You feel dizzy or faint within seconds to 3 minutes of standing. Common causes:

• dehydration from heat, vomiting, diarrhea or not drinking enough
• blood loss
• medicines: blood pressure pills, diuretics, nitrates, alpha-blockers for the prostate, antidepressants
• alcohol
• nerve damage from diabetes or Parkinson's disease
• older age and long bed rest

POTS (postural orthostatic tachycardia syndrome), seen mostly in young women, causes a large rise in heart rate on standing, with dizziness and sometimes fainting.

Heart-related (cardiac) syncope

This is less common but most important to recognize, because it can predict sudden cardiac death:

• Arrhythmias: very slow heart rhythms (heart block) or very fast ones (ventricular tachycardia). Inherited conditions such as long QT syndrome and Brugada syndrome can cause fainting in young people.
• Structural heart disease: aortic stenosis, hypertrophic cardiomyopathy, heart attack.
• Pulmonary embolism: a blood clot in the lungs.

Clues to a heart cause: fainting during exertion or lying down, no warning, palpitations just before, chest pain, a heart murmur, an abnormal ECG, or a family history of sudden death.

Fainting vs other blackouts

Hypoglycemia, stroke or TIA, intoxication and psychogenic attacks can also cause episodes that look like fainting.

How doctors evaluate fainting

The most useful tool is a detailed account from you and any witness: what you were doing, warning signs, how long you were out, what you looked like, and how you recovered.

Every person who has fainted should have:

• a physical exam, including heart sounds for murmurs
• blood pressure lying and standing to check for orthostatic hypotension
• a 12-lead ECG

Further tests depend on the findings:

• blood tests: blood count, glucose, electrolytes, pregnancy test
• echocardiogram if a structural heart problem is possible
• heart rhythm monitoring: a 24-hour Holter, a patch worn for 2 weeks, or an implantable loop recorder for rare episodes
• exercise stress test for faints during exertion
• tilt-table test for unclear recurrent faints
• brain imaging or EEG only if a seizure or neurological cause is suspected

Treatment and prevention

Reflex fainting

• Learn your warning signs and lie down or sit immediately.
• Use counter-pressure maneuvers (leg crossing and muscle tensing).
• Drink 2 to 3 liters of fluid a day and, if your doctor agrees, add some extra salt. Do not do this if you have high blood pressure, heart failure or kidney disease.
• Avoid triggers: long standing, hot crowded places, and dehydration. Lie down for blood tests.
• Medicines (such as fludrocortisone or midodrine) or, rarely, a pacemaker are used for frequent, severe faints.

Orthostatic hypotension

• Stand up slowly, in stages.
• Review medicines that lower blood pressure with your doctor.
• Raise the head of the bed and wear compression stockings or an abdominal binder.

Cardiac causes

Treatment targets the heart problem: a pacemaker for slow rhythms, an implantable defibrillator for dangerous fast rhythms, medicines or ablation, and valve replacement for aortic stenosis.

Driving

Driving rules after fainting vary by state and country and depend on the cause. Ask your doctor before driving after an unexplained faint.

Frequently asked questions

Why do people faint?

Most people faint because a reflex suddenly lowers heart rate and blood pressure, often triggered by standing for a long time, heat, pain, fear or the sight of blood. Less often fainting is caused by low blood pressure on standing, dehydration, medicines, or a heart problem.

Is fainting a sign of something serious?

Usually not. Most faints are harmless reflex faints. Fainting is more concerning if it happens during exercise, while lying down, without warning, with chest pain or palpitations, in older people, or with a family history of sudden death.

What should I do after fainting?

Lie down for 10 to 15 minutes, then sit up slowly. Drink water and eat something if you skipped a meal. See a doctor if it was your first faint, you were injured, or any red flags apply. Get emergency help for chest pain, breathlessness or slow recovery.

How long does fainting last?

A typical faint lasts from a few seconds to about a minute. Most people wake up quickly and are fully alert, though they may feel tired, pale and sweaty for 30 minutes or more. Prolonged unconsciousness or confusion needs emergency care.

Can dehydration make you faint?

Yes. Dehydration lowers blood volume, so blood pressure can drop when you stand up, reducing blood flow to the brain. Heat, exercise, vomiting, diarrhea and alcohol all increase the risk.

Is fainting the same as a seizure?

No. Fainting is caused by reduced blood flow to the brain and recovery is fast. A seizure is abnormal electrical activity in the brain, usually with longer stiffening and jerking, tongue biting and confusion afterward. A few brief jerks during a faint are common and do not mean a seizure.