Hmm it might be pleuralsy (spelling?). I am not guaranteeing anything. I had some chest pain that got worse throughout a day once... hurt the worst when breathing in. I ended up going to the ER b/c I didnt know if was a collasped lung or what since I never had that and didnt know what kind of pain to expect with something like that. It was the day after being discharged from a 2 week hospital stay and after stopping pretty much 6 months of IVs too.
The ER guy comes in and says, "You have pneumonia" and I said, "No, I have Cystic Fibrosis" haha...
After taking it all in, they just said it was Pleuralsy with is like when the lining or something of the lung gets irritated or like inflammed. He said I was still moving air and such and but after the IV pain med of Torredol (Try to never do Morphine or the "d" one which is like 10x the power of morphine but those are narcotics which affect respiratory most)... I did get a Rx for vicotin but never needed it... it pretty much disappeared the next day but I think I took some ibuprofen while it was still hurting.
I imagine walking might have inflammed it more. At the time I was doing the percussor pretty often (more than the vest) so I just let that area "heal" and stuck with the vest for airway clearance.
Hope thats all it is...