Why do people faint? What happens in their bodies that cause them to collapse?

"Fainting is a sudden (and generally momentary) loss of consciousness, or blacking out, due to a lack of sufficient blood and oxygen reaching the brain. The first symptoms a person feels before fainting are dizziness, a dimming of vision, or brown-out and feeling hot. Moments later, the person's vision turns black and he or she drops to the floor (or slumps if seated in a chair).

Factors that influence fainting are taking in too little food and fluids, low blood pressure, hypoglycemia, growth spurts, physical exercise in excess of the energy reserve of the body, and lack of sleep. Even standing up too quickly or being in too hot a room can cause fainting."

http://en.wikipedia.org/wiki/Fainting

Fainting isn't as common as it used to be because women don't wear tight corsets that cramped their lungs and diminished their oxygen supply anymore.

Fainting, frequently called syncope (pronounced /ˈsɪŋkəpi/), is a sudden, and generally momentary, loss of consciousness, or blacking out caused by the Central Ischaemic Response, because of a lack of sufficient blood and oxygen in the brain.

Factors that influence fainting are taking in too little food and fluids, low blood pressure, hypoglycemia, growth spurts, physical exercise in excess of the energy reserve of the body, emotional distress, and lack of sleep. Orthostatic hypotension caused by standing up too quickly or being in a very hot room can also cause fainting.

More serious causes of fainting include cardiac (heart-related) causes such as an abnormal heart rhythm (an arrhythmia), where the heart beats too slowly, too rapidly or too irregularly to pump enough blood to the brain. Some arrhythmias can be life-threatening. Other important cardio-vascular conditions that can be manifested by syncope include subclavian steal syndrome and aortic stenosis.

Fainting can also occur due to submersion in both shallow and deep water.


The first symptoms a person feels before fainting are dizziness; a dimming of vision, or brownout; tinnitus; and feeling hot. Moments later, the person's vision turns black, and he or she drops to the floor (or slumps if seated in a chair). If the person is unable to slump from the position to a near horizontal position, he or she risks dying of the Suspension trauma effect.
http://en.wikipedia.org/wiki/Fainting

Fainting is due to not enough Oxygen in the brain. This can happen from dehydration, in excessive heat and pregnancy at times.

i do it all the time as i have low blood pressure.

Low blood flow equals low oxygen.

not enough oxygen to the brain/
quick lowering of blood pressure
not enough nlood in the brain

I know hypoglycemia results in that

several different ways, but the basic cause is decreased blood flow to the brain ... for example, there is something called a "vaso-vagal response", which is stimulation of the vagus nerve, which causes blood vessels to dilate, blood to pool in the legs, which causes in an abrupt drop in blood pressure, which results in not enough blood getting to the brain ... similarly, police and wrestlers use a "choke hold" or a "sleeper hold", where they put pressure on the blood vessels in your neck, cutting off the blood flow

Dude that happen to me for the first time. Me and my friends decided to get percing and i was getting Plugs. I felt fine the whole time (I never fainted in my whole life) all of a sudden I started feeling hot when she was streachig my ear and than I could start feeling my heart beat and I felt like pukeing... than it got 10x worse. I told everyone I'm about to faint, they ran and got me water, my head started to get light and I started sweating like a bucket of water was dumped over my head and than the room started turning black. I thought they were going to have to call 911. Lucky the girl was a proffesional and she told me to lay me head back. They gave me water Nd some air and wipe the sweat off my face... 5mins later I wAs back to normal with some chills.. It was embaressig because before hand I told her I won't fait I never faint with needles... So long story short I need to finish my other ear up Monday which hopfuly willgo quick and fast. She just needs to streth the whole and sqwezzed the thingy in lol (don't know the name of those plugs percing lol)

But yeah it freaked me out and u literailty see black right before u feel like ur body is going to shut down. It's not fun and really scary