Breathe In, Breathe Out

You just ran after your toddler in what felt like a marathon, you just carried something really heavy up the stairs to your bedroom, or you just thought you heard something enter your house unallowed.  Which ever one of these experiences you’ve ever had, you breathed hard, and gasped for air whether quietly or loudly.  Could you be breathing hard after a long run, because of lack of oxygen or an excess of carbon dioxide?