Why is hyperventilation bad and why do you need to breath in a bag?

Question

I mean, isn’t oxygen good fit your body?

In: Biology

Answer 1

TLDR; “Your body needs the right mix of air to work. Breathing into a bag helps keep the right mix”
Hyperventilation (rapid breathing or deep breathing, often caused by psychological stress) causes an imbalance of oxygen and CO2 (too little CO2) which leads to constriction of blood vessels, most importantly, to/from the brain. Should your blood vessels constrict too drastically for your brain’s oxygen requirements (i.e. strenuous activity while hyperventilating) you could pass out due to lack of oxygen to the brain. This is why doctors advise against taking a bunch of deep breaths before swimming distances underwater (military doctors). Breathing into a bag allows more CO2 into the lungs, helping maintain the O2-CO2 balance in the bloodstream, thus keeping blood vessels open and you conscious.