Fainting or passing out is a common phenomenon – about 1/3 people faint once in their whole life. People faint when the brain fails to receive sufficient amounts of blood and oxygen. Normally, oxygen is delivered to the brain by 750 ml of blood every 60 seconds. If this amount goes down, then a person lacks the correct amount of oxygen. Passing out usually is the loss of consciousness for a while.

What Happens When You Pass Out?

Different reasons can make someone faint. Commonly, people faint because of a condition known as vasovagal syncope. The human body is programmed to produce adrenal and cortisol hormones when a person encounters a frightening or uncomfortable situation, for example, when attacked by a dog. This results in faster heartbeat and a constriction of the blood vessels. With the higher blood pressure, your brain and body muscles receive more oxygen. Of course, this state is not permanent. Soon after, your body will relax back to normal. Your blood vessels will dilate and your heart will slow down. Normally, this process should take the person back to their original state. In some people, the return to normal goes overboard and the person ends up in an opposite state. The brain will therefore receive less blood, and consequently, less oxygen. The process of fainting usually doesn't last long.

What Causes Fainting?

After the answer to "what happens when you pass out?" here are some common causes of fainting in daily life.

1.   Vasovagal Syncope

Vasovagal syncope can result from environment factors such as heat and crowd. Stress, threat, fatigue, dehydration are also possible culprits. Sometimes, standing too long can also lead to fainting.

2.   Situational Syncope

This occurs in a similar way to vasovagal syncope, but only under certain situations. For example, it can occur due to forceful coughing and swallowing in people with throat disease. Postprandial fainting happens when the blood pressure of elderly people drops about an hour after eating.

3.   Postural Syncope

Postural syncope occurs when a person faints on standing. Usually, the person will be perfectly active and alert when seated or lying down. But when the person stands up, the blood flow to the brain is immediately cut, making the person pass out. This results from a sudden drop in blood pressure on standing up. Dehydration, blood loss, and heat exhaustion can lead to lower amounts of blood in circulation. Medications can also cause postural syncope fainting if it impairs circulatory reflexes. This can also be caused by disorders in the nervous system, congenital problems or diabetes.

4.   Cardiac Syncope

What happens when you pass out? What can cause you to faint? Heart disease can cause a person to pass out. This can even result in death depending on the level of severity of the condition. The possible heart conditions include cardiac rhythm abnormality, blocked blood flow and heart failure.

5.   Neurological Syncope

Fainting can also be caused by conditions in the nervous system. These include strokes, transient ischemic attacks and migraines.

6.   Psychogenic Syncope

This results from an anxiety disorder. Sometimes, people pretend to faint to lower stress, or to avoid unknown gain. This is rare and should only be decided after all other causes of fainting have been ruled out.

When to Worry 

You need to worry fainting under these circumstances:

• When fainting occurs frequently in short periods of time
• If you faint while exercising
• If it happens suddenly without any warning
• If it happens when one is lying down
• If you are often short of breath
• If you also have chest pains
• If your heart is beating irregularly
• If you also experience numbness on a section of your body
• If you does not recover within a few minutes
• If you are pregnant
• If you are over 50 years of age
• If you also have diabetes
• If you have issues with sight and verbal communication
• If you have trouble controlling the bladder and bowel
• If you have previously been diagnosed with heart disease

What to Do If You See Someone Fainting

Besides knowing "what happens when you pass out?" you also need to learn the first aid which is usually life-saving. Take the following steps when you see somebody fainting.

• Get the patient to a position flat on the back, facing up.
• Make sure the patient’s airway is not being blocked.
• Check for breathing, coughing or movement. 
• Check for the patient’s bleeding, and control it if there is any.
• Have the patient’s legs 12 inches higher compared to the rest of the body. This will increase the amount of blood flowing to the brain.
• Loosen all tight clothing.
• Do not let the patient get up immediately after he/she recovers.
• If the patient still remains unconscious after one minute, keep him/ her in the same position and get medical help. Start CPR if necessary.