Fainting

Fainting happens when your brain doesn't get enough oxygen, causing you to pass out. Most people recover quickly.

Fainting is caused by reduced blood flow to the brain, often due to low blood pressure. After you lose consciousness (pass out) and fall or lie down, more blood can flow to your brain so you wake up again. Usually fainting happens for a reason, such as if you have been standing for a long time in a hot place, or if you're in pain. 

 Before you faint, you might experience a range of symptoms or warnings. These can include:

• looking pale
• feeling warm
• feeling light-headed, sick (nauseous) and sweaty
• experiencing a spinning sensation
• losing some or all of your vision
• having trouble hearing.

 Some people know they are going to faint because they have these symptoms beforehand, this is known as pre-syncope. 

As soon as you begin to feel faint, lie down and raise your feet so they’re higher than your head. If you can’t lie down, sit down and put your head between your knees. This will help to increase the flow of blood to your brain and may prevent you from fainting. Don't get up too quickly, and if you feel faint again, get back down. Get some fresh air.

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• Sit up slowly and take it easy for the rest of the day, you may feel tired for a while.
• Let somebody know that you’ve fainted so they can keep an eye on you and call for help if it happens again.
• Avoid strenuous exercise for a couple of days.
• Drink plenty of fluid to stay well hydrated.
• Avoid alcohol as it can lower your blood pressure.
• Keep taking your usual medicines unless you have been advised not to by your healthcare provider.
• Avoid hot baths or showers.
• Avoid taking sleeping tablets or sedatives unless advised by a healthcare provider.

Fainting can be due to a number of causes.

Vasovagal reflex

Most often, fainting is caused by the vasovagal reflex, where blood pools in the lower body and less blood, and oxygen, goes to the brain. This can be brought on by:

• stress or emotional distress
• pain, especially severe pain
• low blood glucose levels
• fear
• standing up too quickly
• standing for a very long time, especially in hot places and if you are dehydrated
• holding your breath
• seeing blood, having an injection or getting blood drawn.

In some situations, fainting may occur as a reflex response to specific triggers. These include:

• coughing, sneezing, laughing or swallowing
• straining when passing a bowel motion (pooing)
• urinating (for men standing up to wee)
• sudden abdominal pain
• eating a meal
• blowing a brass instrument
• lifting weights
• wearing a tight collar, twisting your neck hard or otherwise putting pressure on your carotid artery if you are older person.

Orthostatic hypotension

Fainting can also be caused by a drop in blood pressure when you stand up too fast. This is called orthostatic hypotension and is more common in older people. It can be made worse by:

• dehydration
• taking medicines that lower blood pressure, eg, diuretics
• some conditions, eg, Parkinson's disease. 

More serious causes

In some cases, fainting may be caused by more serious medical problems such heart or lung problems, stroke, or epilepsy.  

See your healthcare provider if you’ve had a fainting episode. To find the cause of your fainting, they will do a physical examination and ask questions about how and when you fainted. Depending on what the physical examination shows, your healthcare provider may want to do tests such as blood tests, ECG or EKG, heart checks, a tilt table test or a CT scan.