2 of the biggest reasons for low breathing or shortness of breathe are a condition called Dyspnea - check it out I think you will agree!
Also the other point - my first thought - was anxiety breathing! When you have anxiety - which I have suffered from for years - you are constantly catching your breathe and noticing yourself breathing - which you shouldn't, just like blinking - it can happen at ANY time for no apparent reason! NOW when you read about Dyspnea - do NOT instantly jump to the cancer or heart part OK? these are just reasons for it! You do NOT have eitther of these - these are REALLY major and you would not have had such a MAJOR disease like these for all of these years. Check out the other reasons why, also look into Anxiety and Breathing - see which one rings truer!
I'm thinking this is what you're asking - sorry if i'm way off base.
<3 Katie
I had a very similar problem. For months I had trouble getting a full breath and felt tightness in my chest when it got bad. I used to always make myself yawn just for the relief that a deep, full breath would bring but it was only a series of small temporary solutions.
After several doctors visits and thorough examinations (chest xray, CT scan, pulmonologist tests, stress tests, etc) I found the problem was not my lungs or heart but Acid Reflux. I eventually got an endoscopy exam and the doctor determined that I had a Hiatal Hernia that was caused by the reflux and causing pressure to form in my chest/lungs area. He prescribed me Omeprazole (Prilosec) which began to help greatly within a few days. I started with the over-the-counter Prilosec and then eventually got a prescription for a higher dose that would also be a lot cheaper for me to take for a few months.
Hope this helps!