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’s no underlying medical condition causing you to faint, you may not need any treatment.

Fainting isn’t usually a cause for concern, but it can sometimes be a symptom of a serious medical problem. If you have no previous history of fainting and you’ve fainted more than once in the past month, you should talk to your doctor.

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
  • hyperventilation
  • dehydration
  • 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
  • seizures

Medications that can cause your blood pressure to drop also increase your chance of fainting. These include certain medications used to treat:

  • high blood pressure
  • allergies
  • depression
  • anxiety

If turning your head to one side causes you to faint, it’s possible that the sensors in the blood vessel in your neck are extra sensitive. This sensitivity can cause you to faint.

You’re also more likely to faint if you have any of these conditions:

  • diabetes
  • heart disease
  • atherosclerosis
  • an irregular heartbeat, or arrhythmia
  • anxiety or panic attacks
  • chronic lung disease, such as emphysema

There are several types of syncope. Three common types include:

  • Vasovagal syncope. Vasovagal syncope involves the vagus nerve. It can be triggered by emotional trauma, stress, the sight of blood, or standing for a long period of time.
  • Carotid sinus syncope. This type 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. This type occurs due to straining while coughing, urinating, moving your bowels, or having gastrointestinal problems.

You should call 108 or your local emergency services 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, or has a history of heart disease
  • 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