Most people have noticed that when someone is very anxious they hyperventilate. We have all seen images of people breathing into a brown paper bag to  calm them down. What is happening is that when the person over breathes, they loose too much carbon dioxide. This causes them to become more anxious and they over breathe more...creating a spiraling effect in their panic and breathlessness. Carbon dioxide in NOT a waste gas and is very important to the functioning of our bodies systems. If levels get too low we could faint (until levels restored.) By learning to breathe correctly you can control anxiety and panic attacks. check out The buteyko method to see how it works.  Breathe Well! Be Calm :)