Fainting happens when you lose consciousness for a short amount of time because your brain isn’t getting enough oxygen. The medical term for fainting is syncope, but it’s more commonly known as "passing out." A fainting spell generally lasts from a few seconds to a few minutes.
Feeling lightheaded, dizzy, weak, or nauseous sometimes happens before you faint. Some people become aware that noises are fading away, or they describe the sensation as "blacking out" or "whiting out." A full recovery usually takes a few minutes. If there is no underlying medical condition causing you to faint, you may not need any treatment.
Fainting usually isn’t a cause for concern, but it can be a symptom of a serious medical problem in some cases. If you have no previous history of fainting and you have fainted more than once in the past month, you should talk to your doctor.
Causes of fainting
In many cases, the cause of fainting is unclear. Fainting can be triggered by a number of factors, including:
- fear or other emotional trauma
- severe pain
- a sudden drop in blood pressure
- low blood sugar due to diabetes or from going too long without eating
- hyperventilation (rapid, shallow breathing)
- standing in one position for too long
- standing up too quickly
- physical exertion in hot temperatures
- coughing too hard
- straining during a bowel movement
- consuming drugs or alcohol
Medications that can cause your blood pressure to drop also increase your chance of fainting. These include certain medicines to treat high blood pressure, allergies, depression, and anxiety.
If turning your head to one side causes you to faint, it’s possible that the bones in your neck are pinching a blood vessel.
You’re more likely to faint if you have any of these conditions:
- heart disease
- irregular heartbeat (arrhythmia)
- anxiety or panic attacks
- chronic lung disease (such as emphysema)
Types of fainting
There are several types of syncope (fainting). The following list includes three common types:
- Vasovagal syncope can be triggered by emotional trauma, stress, the sight of blood, or standing for a long period of time.
- Carotid sinus syncope happens when the carotid artery in the neck is constricted, usually after turning your head to one side or wearing a collar that’s too tight.
- Situational syncope occurs due to straining while coughing, urinating, moving your bowels, or having gastrointestinal problems.
How to prevent fainting
If you have a history of fainting, try to learn what is causing you to faint so you can avoid those triggers. Always get up slowly from a sitting or lying down position. If you tend to feel faint at the sight of blood when getting your blood drawn or during other medical procedures, tell your doctor. Your doctor can take certain precautions to prevent you from fainting. Lastly, don’t skip meals.
Feeling lightheaded and weak and having the sensation of spinning are warning signs of fainting. If you notice any of these signs, sit and put your head between your knees to help get blood to your brain, or lie down to avoid injury due to falling. Don’t stand up until you feel better.
What to do when someone faints
When someone near you faints, you can encourage blood flow to their head by raising their feet above the level of their heart. Alternatively, you can have the person sit with their head between their knees.
Loosen tight collars, belts, or other tight clothing. Keep the person lying down or sitting for at least 10 to 15 minutes. A cool, quiet place is best. A cool drink of water may also help.
If the person isn’t breathing, call 911 immediately.
When is fainting an emergency?
You should call 911 immediately if someone has fainted and:
- isn’t breathing
- doesn’t regain consciousness within a few minutes
- has fallen and sustained an injury or is bleeding
- is pregnant
- has diabetes
- has no history of fainting and is over age 50
- has an irregular heartbeat
- has complained of chest pain or pressure
- has convulsions or has injured their tongue
- has lost bowel or bladder control
- has difficulty with speech or vision
- remains confused or disoriented
- is unable to move their limbs
Follow the instructions of the 911 operator. You may need to perform rescue breathing or CPR while awaiting help.
Tests and diagnosis
If your health is good overall and you have fainted only once, you probably don’t need to see a doctor. However, if you have no prior history of fainting and have fainted multiple times, your doctor will want to determine if an underlying medical condition is the cause.
Tell your doctor about the specific circumstances of your fainting spell, such as what you were doing and how you felt immediately before fainting. Be prepared to give your doctor a complete medical history, including information about previously diagnosed conditions and any prescription and over-the-counter medications you take.
Depending on the findings from a physical examination, your doctor may order additional tests. Your doctor may order blood tests to check for chemical imbalances and anemia in particular. Tests to check for heart problems include:
- Holter monitor, which is a portable heart-monitoring device that you wear for 24 hours and sometimes longer
- echocardiogram, which is a test that uses sound waves to produce a moving picture of your heart
- electrocardiogram (ECG), which is a test that records the electrical activity of your heart
- electroencephalogram (EEG), which is a test that measures the electrical activity of your brain
- head CT scan, which is an imaging study that checks for bleeding in the brain
Treatment for fainting
Treatment for fainting will depend on your doctor’s diagnosis. If there are no underlying medical conditions that are causing you to faint, you generally won’t need treatment and the long-term outlook is good.
Written by: Ann Pietrangelo
Medically reviewed on Sep 15, 2015 by Steven Kim, MD