Fainting, also called “passing out” or “blacking out”, is a brief, sudden loss of consciousness. You lose muscle tone and you may fall. You will not be aware of what is happening to you until you start to recover. Usually, you will recover completely in a few seconds or minutes.
Fainting is not usually caused by a serious or life-threatening medical problem. However, if you have heart disease, or you faint during even mild exercise, the cause may be serious and you need prompt medical care.
Fainting is fairly common. The medical term for fainting is syncope.
What is the cause?
Fainting may be caused by.
Severe or sudden pain, or severe stress, embarrassment, or seeing something that scares or upsets you
A brief drop in your blood pressure, which can happen when you take a deep breath and push down but don’t allow yourself to breathe out. You may do this, for example, when you urinate or have a bowel movement, cough hard for a long time, or lift someone.
Being dehydrated, which means losing too much fluid from your body. This happens more often if you are vomiting, have diarrhea, or sweat a lot.
Less blood being pumped to the brain, which may be caused by:
A very fast or very slow heartbeat
A heart attack that damages the pumping muscle
Abnormal heart valves
Standing for a long time, especially with your knees locked (straight), or standing up quickly after sitting or lying down
Low blood sugar. For example, if you have diabetes, your medicines might make your blood sugar too low.
Some medicines, such as diuretics (water pills) and blood pressure-lowering medicines
What are the symptoms?
You may faint suddenly without any other symptoms. Or at first you may feel nauseous or sweaty. If your fainting is caused by a heart problem, you may feel like your heart is beating fast or skipping beats. You may feel short of breath, or you may feel pressure or pain in your chest before you faint.
How is it diagnosed?
Your healthcare provider will ask about your symptoms and medical history and examine you. How you felt before and after you fainted are important facts that can help your provider diagnose the problem.
Tests may include:
An ECG (also called an EKG or electrocardiogram), which measures and records your heartbeat. You may have an ECG while you are resting or while you exercise on a treadmill. You may also be asked to wear a small portable ECG monitor for a few days or longer.
An echocardiogram, which is an ultrasound test of the heart to check for problems with the heart muscle or the heart valves
A chest X-ray
A tilt table test to measure your blood pressure while you lie on a table that is gradually tilted toward the head-up position
An electrophysiology study, which is a test of the electrical system of the heart
How is it treated?
The treatment of fainting is based on the cause. If you have heart problems, or low blood pressure, treating those problems will also treat fainting. Your provider may change the medicine you are taking, or recommend that you wear support hose, which support the muscles in your legs and help prevent pooling of blood. If you stand a lot for work or school, keep your knees slightly bent when you stand. This helps blood return to your heart and prevents fainting.
How can I take care of myself?
Follow the full course of treatment prescribed by your healthcare provider. In addition:
Drink plenty of liquids, especially in hot weather.
If you have diabetes, it is important to control your blood sugar.
Take care of your health. Try to get at least 7 to 9 hours of sleep each night. If you smoke, try to quit. If you want to drink alcohol, ask your healthcare provider how much is safe for you to drink. Learn ways to manage stress. Exercise according to your healthcare provider’s instructions.
Ask your provider:
How and when you will hear your test results
If there are activities you should avoid and when you can return to your normal activities
How to take care of yourself at home
What symptoms or problems you should watch for and what to do if you have them
Make sure you know when you should come back for a checkup. Keep all appointments for provider visits or tests.
Developed by RelayHealth.
Adult Advisor 2015.1 published by RelayHealth. Last modified: 2014-10-31 Last reviewed: 2014-10-30
This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.
Syncope(Fainting).(2012). American Heart Association. Retrieved 10/2014 from
Alboni, P, Brignole, M, Menozzi, C, et al. Diagnostic value of history in patients with syncope with or without heart disease. J Am Coll Cardiol 2001; 37:1921.
Benditt, DG. Syncope Management Guidelines at work: first steps towards assessing clinical utility. Eur Heart J 2006; 27:7.
Brignole, M, Alboni, P, Benditt, DG, et al. Guidelines on management (diagnosis and treatment) of syncope–update 2004. Europace 2004; 6:467.
Kapoor, WN. Evaluation and outcome of patients with syncope. Medicine 1990; 69:160.
National Institute of Neurological Disorders and Stroke. NINDS Syncope Information Page. US Dept of Health and Human Services, National Institutes of Health, National Institute of Neurological Disorders and Stroke. 10/4/11. Accessed 10/25/12 from http://www.ninds.nih.gov/disorders/syncope/syncope.htm.
Shen, WK, Decker, WW, Smars, PA, et al. Syncope Evaluation in the Emergency Department Study (SEEDS): a multidisciplinary approach to syncope management. Circulation 2004; 110:3636.