You know... I used to have this problem that my doctor said was basically a partial lung collapse. He said, in simple terms, small portions of my lung would get stuck together (hurt like hell to breathe in) and sooner or later it could trigger a full collapse. He attributed it to asthma (thicker mucus is a side effect) and this was long before I started smoking. It continued while I smoked, but I can't remember the last time I had the problem (year and a half of vaping)...