What does it mean when your chest always hurts when breathing deep?

Two prior answers. . This sounds like overnight something has affected your lung function, breathing pattern, or lung lining or chest --which inflamed can cause pain upon taking a deep breath--, or chest wall muscles. Perhaps, position while sleeping, viral illness, overusing your upper body muscles the day before (did you start or do excessive exercise the day before). If persists, like anything else, c the doc.