Hurts to breath in deeply?

This just started today, and I have pain only when i breathe in deeply, and its right near the center off my rib cage, just to the sides of the sternum.I have no other signs of illness, no cough, or wheezing, no shortness of breath, and no difficulty breathing regularly. When I do cough, it is not painful. Could this just be the result of sleeping in an awkward position? As i said, there were no problems until this morning.