what causes people to faint or pass out
Many different conditions can cause fainting. These include heart problems such as irregular heart beats, seizures, low blood sugar (hypoglycemia), anemia (a deficiency in healthy oxygen carrying cells), and problems with how the nervous system (the body's system of nerves) regulates blood pressure.
Vasovagal syncope is a common cause of fainting. The vagus nerve is overstimulated and causes the body's blood vessels to dilate and the heart to slow down. This anti-adrenaline effect decreases the ability of the heart to pump blood upward to the brain against gravity. Without blood flow, the brain turns off.
If the syncope is prolonged, it can trigger a seizure. You may suffer from a simple fainting spell due to anxiety, fear, pain, intense emotional stress, hunger, or use of alcohol or drugs. Most people who suffer from simple fainting have no underlying heart or neurological (nerve or brain) problem.