When falling through the air or flying at incredibly fast speeds, it's possible for even the most experienced air sports athletes to pass out. These blackouts can have catastrophic effects, which is why it's best to follow the rules and precautions associated with air sports before you take off.
If you're prone to blackouts, you shouldn't be flying. Increased risk comes if you're overweight, epileptic, addicted to drugs or alcohol or have heart disease. Even if you're not, people can still be surprised by how their bodies react to high altitude or the affect of high speeds [source: Medicine Net].
Passing out while falling through the sky is nobody's idea of a good time, and it's one of the most terrifying things that can happen in the air. This is why people partner up when they first hit the skies, because no amount of training can predict exactly how a person's body will react to the increased stress.