Jason,
I've noticed that if I am coming down with a bad cold, the BEST thing I can do for myself is hike a winter 4K. All the crap in my throat/lungs is hacked up during the hike, and when I come back I am cured.
This has happened three times, seems to be something about that nice, clean, cold mountain air...it cleanses my lungs, or some such thing.
Maybe the same thing is happening to you, but your crap is being coughed up after instead of during?
Of course, I'm not a doctor, yada yada yada.
PS -- not a smoker, never have been.
PPS -- obviously, as I'm sure you already know, only a doctor can give you a real sense of what's going on.