I have lots of chest pain and my family doctor said that it's due to very strong anxiety and shallow breathing. It's nice to have those words from more than one doctor, isn't it?
I use a c-pap machine at night. I have to be very careful about pain meds. The last pain shot I got in an ER worked so well, I stopped breathing normally. They had to put oxygen on me until the initial effect of the shot went away.
Another word about the shallow breathing - we did that as kids when we hid from our abuser. Another way to stay in hiding as long as we could.