Fainting isn’t fun, and when it’s happening to you, or when it’s happening to someone else, It is scary, and it is unpleasant, and why, why do we do that? When you faint, it’s because your nervous system went haywire, and your brain wasn’t getting enough oxygen. A brain requires oxygen like a computer requires electricity and that oxygen is carried to your brain by blood. A lot of blood. About 750 mL of blood flowing through your head every minute. If you suddenly decrease that oxygen-rich blood flow, you get a temporary loss of consciousness known to doctors as syncope, and to the rest of us as fainting. There are lots of different, and sometimes serious medical conditions that can make someone faint, but the kind that we’re talking about today, the kind that makes someone drop at the sight of blood, is called Vasovagal Syncope. It’s named after the vagus nerve, which goes from your brain all the way down through your body ending at your colon. It’s part of your autonomic nervous system, which regulates your body’s involuntary functions. The vagus nerve in particular manages your heart rate and blood pressure, but it’s also responsible for recalibrating your body after you experience a so-called fight-or-flight response. When something particularly shocking or unpleasant happens, your body goes into survival mode. You release stress hormones, like adrenaline and cortisol, which make your heart beat faster and constrict your blood vessels, raising your blood pressure and sending more blood and oxygen to your muscles and brain. Heart pumping and muscles primed, you’re ready to either fight or run away. But it’s all very temporary. After the initial shock, your vagus nerve kicks in, telling your heart to slow down. It also tells your blood vessels to open back up, and get your blood pressure back to normal. In some people this recalibration goes temporarily overboard, like the pendulum swinging back in the other direction. So if the vagus nerve overcorrects and the heart rate drops too much blood pressure drops too low, and the brain’s oxygen supply is suddenly interrupted. [It’s] like unplugging that computer. You black out, you lose muscle control, and you tumble down like a Jenga set. This kind of fainting doesn’t usually last long, though. Within a matter of seconds, your vagus nerve corrects the error, and returns your heartbeat and blood pressure to normal. You regain consciousness, open your eyes, and try to figure out what the heck just happened. This question came our way from a Patreon Patron known only to us as: Fan From Singapore. If you’d like to submit a question to be answered you can go to patreon.com/scishow and don’t forget to go to Youtube.com/scishow and subscribe for more answers all the time. The stuff that you’re curious about. I know you are.