Healthy Living

Understanding Fainting: What Causes It?

Mar 10 2023

Fainting, or syncope, is a sudden loss of consciousness without warning caused by a decrease in blood flow to the brain. It can last a few seconds to a few minutes and is usually followed by a quick recovery.

You may faint if you’re in pain, have a sudden drop in blood pressure or simply don’t get enough blood to your brain. You can also faint if you stand up too fast or if you hold your breath for too long.

Most of the time fainting is nothing to worry about. However, it also can be a sign of something serious. 

Call 911 or go to the emergency room right away if:

  • You’ve never fainted before
  • You’re older than 50 and faint while standing up
  • You feel lightheaded or weak before you faint
  • You have heart disease
  • You have diabetes and feel very sick after fainting

What are the causes of fainting?

There are many reasons for fainting. Sudden collapse causes can be linked to not getting enough oxygen to the brain, low blood sugar (hypoglycemia), dehydration, overheating and heart problems. Some medicines can also cause fainting.

Another cause of fainting is vasovagal syncope. This occurs when the vagus nerve, which helps control heart rate and blood vessel constriction, is stimulated in a way that slows the heart rate and dilates blood vessels. This is also known as neuro-cardiogenic or vasodepressor syncope.

Vasovagal syncope can be triggered by:

  • Emotional stress
  • Pain
  • Standing for a long time, especially in hot weather
  • Exposure to blood or blood-drawing procedures

Alcohol use can also lead to vasovagal syncope because it causes dehydration and lowers blood sugar levels.

There are also a variety of known medical conditions that cause fainting. Some of the most common are listed below.

  • Abnormal heart rhythms (cardiac arrhythmias)
  • Slow heart rate (bradycardia)
  • Fast heart rate (tachycardia)
  • Low blood pressure (hypotension)
  • High blood pressure (hypertension)
  • Heart valve disease
  • Enlarged heart muscle (hypertrophic cardiomyopathy)
  • Heart failure
  • Narrowing of the main artery from the heart (aortic stenosis)

Symptoms of fainting may include dizziness and lightheadedness before you faint. You may feel clammy and look pale, and you may have blurred vision or hear ringing in your ears.

If you are about to faint, lie down on the floor. If you have time, take off tight clothing so you can breathe more easily.

Are there different types of fainting?

Yes, there are. The most common type of fainting is called vasovagal syncope. Vasovagal syncope, as discussed above, occurs when you have a sudden drop in blood pressure, often brought on by a trigger such as the sight of blood or extreme emotional distress.

Another type of fainting is situational syncope. Situational syncope happens when you faint during specific situations, such as coughing, urination or swallowing.

Carotid sinus syncope occurs when there’s abnormal sensitivity in the carotid artery in your neck. If you have this condition, pressure on this area, such as from wearing a tight collar or turning your head to one side, may cause you to faint.

Orthostatic, or postural, hypotension is a form of low blood pressure that happens when you stand up from sitting or lying down. Gravity causes blood to pool in the lower half of your body, so less blood returns to your heart. The reduced blood flow to your brain can cause you to faint.

The after-effects of fainting are usually:

  • Temporary confusion
  • Memory loss
  • Dizziness
  • Lightheadedness
  • Nausea
  • Pale skin color
  • Headaches

How can I prevent fainting?

There is no evidence that fainting episodes are inherently dangerous, but they can be frightening, especially when you experience fainting in the shower or fainting and shaking. Fainting can also cause injuries from falls, including broken bones and head injuries.

So, to prevent fainting:

  • Wear loose-fitting clothing in hot weather
  • Don’t skip meals or restrict food intake, especially when you’re standing for long periods of time.
  • Get up slowly after sitting or lying down
  • Avoid sudden changes in temperature
  • Avoid situations in which you may overheat, like hot baths
  • Eat, frequent small meals and avoid large meals
  • Drink enough fluids, especially in hot weather. Don’t skip meals or limit fluid intake to help you lose weight. Both can cause low blood sugar levels and make you feel lightheaded or dizzy
  • Avoid alcohol, illegal drugs and caffeine. These substances can worsen some medical causes of fainting
  • Sit quietly for a few minutes afterwards and make sure someone stays with you until you feel completely recovered

If you feel lightheaded, sit or lie down right away, especially if you’ve just stood up after sitting or lying down. If you feel as though you’re about to faint, lie down with your feet elevated — about a foot above the level of your heart. This position can help restore blood flow to your brain.

When to reach out to your health care provider

If you faint more than once, or if you experience other symptoms such as dizziness, seizures, chest pain or shortness of breath before or after a fainting episode, contact your health care provider.

If you have a family history of heart conditions that can cause fainting, discuss this with your provider as well so they can investigate the cause.

Learn about the primary care services we offer at Bon Secours.

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