No, it's because we need to breathe. Your body needs oxygen. Air pressure has little to nothing to do with it as far as I know.
Most likely obese, but it depends on the female's height and weight
False, digestion begins in the mouth.
i highly doubt it because AIDS is mainly transmitted sexually or if there person shares a needle. in other words if you are using something that has already been used from someone else who has AIDS and injecting in yourself, then yes definitely you would have the chances of AIDS