Breathing

That happened with me as well, at first I thought I had lung cancer. This was early 2005 and I was 15.

I don't think I have anxiety, or a severe case anyway and it slowly died and it rarely comes, unless sometimes I sleep on my side.

I have not had this issue with breathing but do have an issue with eating, swallowing to be precise! I am so deathly afraid of choking (due to severe anxiety) that I pay such close attention to my swallow timing that I actually cause myself to not be able to swallow my food. The trick is to say to yourself my body does this on it's own and I do not need to keep track of it. Breathing and swallowing are natural reflexes that your body does without thinking about it. This does not always help but most times it kicks the worry for the time being. Otherwise I would consider talking to your doctor about the amount of anxiety you are experiencing and they may prescribe something for you or develop an excercise to help you overcome the issue.