Before you can truly take a real, deep breath, you have to remember to do one important thing: give away all the air you’ve already got. If you’re like most people, you’ve been breathing short, shallow puffs from your chest for as long as you can remember, so you don’t have the muscle memory to take deep, belly breaths when you really need them.
To see where you breathe from, place one hand on your chest and the other under your belly button. Most people find that, when they inhale, their chest hand moves and their belly hand doesn’t–meaning that they’re using chest muscles, rather than the diaphragm, to move the air in. That shallow kind of breathing contributes to nervousness and stifles the calming, parasympathetic system.
That parasympathetic system is what you need to be comfortable on a skydive. When it’s shut down, you can get chest pain or heaviness (because you’ve ratcheted the muscles of your chest super-tight), dizziness (because shallow breathing can produce the same symptoms as hyperventilation) and arrhythmia or rapid heartbeat.