Summarize the following:
Holding your breath deprives your brain of oxygen. Your body is used to a steady flow of fresh oxygen; indeed, you need to breathe it almost constantly to survive. If you hold your breath, you deprive yourself of oxygen, and your brain quickly descends into "crisis mode". If you hold your breath until you feel uncomfortable—even for just a matter of seconds—you will be able to make yourself lightheaded. Don't hold your breath for too long, or you might pass out. Whatever you do, do not deprive yourself of oxygen in a way that you can't manually override. You're playing with your life here. Only hold your breath if you are able to resume breathing again at a moment's notice. This means:  Do not seal your head inside an airtight container, like a bag or a plastic wrap. Certainly don't plug your nose and your mouth at the same time. You run a high risk of suffocating. Do not try to make yourself lightheaded underwater. If you pass out underwater, you might not be able to bring yourself to the surface – and you might drown. Do not try to make yourself lightheaded while you're doing anything that requires your full attention. Don't do this while riding a bike or driving a car. Don't do this while standing on the edge of a high place. You might crash; you might fall. Your vision may go dark, and your brain may feel temporarily empty. The sensation might be overwhelming; you might even pass out. Don't try to walk until your head clears. Make sure that you are always in control of whether or not you can breathe – otherwise you risk brain damage or even death.
Hold your breath. Be very careful. Prepare to see stars and feel very dizzy.