What are the most common causes of fainting?

Fainting is usually not a sign of a serious health problem, but it can be.

The most common reason for fainting is a sudden drop in blood pressure, which reduces blood flow and oxygen to the brain. There are many reasons why a drop in blood pressure could lead to a temporary loss of consciousness:

• Cardiac syncope: This type of syncope involves fainting due to a heart problem. Many heart conditions can affect how much oxygenated blood is pumped to the brain.
• Carotid sinus syncope: This type of syncope can happen when the carotid artery in the neck is constricted (pinched). The carotid artery is a blood vessel that supplies the brain. This type of fainting can occur when someone wears a very tight collar, stretches or turns the neck too much, or has a bone in the neck that is pinching the artery.
• Situational syncope: Certain bodily movements or functions can naturally cause a drop in blood pressure that may lead to fainting spells. Examples include when a person pees, poops, coughs or stretches.
• Vasovagal syncope: This can occur when a person experiences a stressful event. Examples include the sight of blood, emotional stress, physical or emotional trauma, or pain. The stressful event stimulates a bodily reflex called the vasovagal reaction. The heart slows down and pumps less blood, so blood pressure drops. Then the brain doesn’t get enough oxygenated blood, and the person faints.

Are there other reasons why I fainted?

Other possible causes of passing out include:

• Certain medications such as diuretics (water pills), calcium channel blockers and angiotensin-converting enzyme (ACE) inhibitors (often used for high blood pressure). Other examples include nitrates for heart disease, antipsychotics for mental health disorders, antihistamines for allergies and narcotics for pain.
• Dehydration or overheating.
• Neurologic condition, such as a seizure disorder, although this is rare.
• Sudden drop in blood sugar, as may happen in a person with diabetes.

Activities that may cause you to pass out include:

• Skipping too many meals.
• Hyperventilating (breathing too fast).
• Working, playing or exercising too hard, especially in the heat.
• Standing up too quickly.
• Using alcohol, marijuana or illegal drugs.

What should I do if someone faints?

If someone loses consciousness:

• Make sure the person’s airway is clear.
• Check that the person is breathing.
• Check that the heart is beating.
• Call 999 or seek immediate medical attention if needed.

When someone faints and then wakes up:

• Encourage them to sit down or lie down for 10 to 15 minutes (sometimes longer, until symptoms pass).
• Check for any injuries that might need medical attention (such as a head injury or a cut).
• Suggest that they sit forward and lower their head below their shoulders and knees.
• Offer ice or cold water.

Can I prevent fainting?

Pay attention to specific activities or situations that trigger fainting. When you know what causes your fainting spells, you can take steps to avoid them. For example, if getting up too quickly sometimes makes you pass out, learn to take your time standing.

If you notice how you feel just before you faint, you can try certain strategies to prevent it:

• Make a fist.
• Tense your arms.
• Cross your legs.
• Squeeze your thighs together.

When should I discuss fainting with my doctor?

If you faint once and are in good health otherwise, you probably don’t need to talk to a healthcare provider. But seek medical attention if you:

• Are injured due to a fainting fall.
• Have repeat, frequent fainting spells.
• Take longer than a few minutes to regain consciousness.

Talk to a healthcare provider if you pass out and have any of the following symptoms:

• Blurry vision.
• Chest pain.
• Confusion or trouble talking.
• Irregular heartbeat.
• Loss of control with peeing or pooping.
• Shortness of breath.

Also report any loss of consciousness to a healthcare provider if you:

• Are pregnant.
• Have diabetes.
• Have a problem with your heart or blood pressure.

Fainting, or passing out, is usually caused by a drop in blood pressure, which reduces blood flow and oxygen to the brain. Most fainting spells are nothing to worry about. But talk to a healthcare provider if you lose consciousness repeatedly or have any other symptoms.