I had the same symptoms and my boss (surgeon) ordered a ct of my ribs to rule out recurrent rib fractures from my accident 4 yrs ago! the pain was that bad.
WHAT it was/is, is the costocartilage of your ribs which are connected to your cervicle/thoracic spinal nerves(c5 to t9) acting up. When you have a flare it causes "angina" pain and shortness of breath. I seriously thought I was having a heart attack or had a punctured lung the pain & shortness of breath was that bad (I'm only 45 & in really good health otherwise) They also discovered I have a intervertebral herniations from t5 all the way down the thoracic column, BESIDES TOS.
I took alot of anti-imflammatory meds and muscle relaxants and used the heating pad. This helped to settle it down. As hard as it was I had to relax and try not to be tense, as this made it worse. I did some very slow breathing exercises and stretches.
I think I was doing alot of lifting and this set it off. I just need to be very careful of what/how much I lift and the way I carry things. Loads don't always need to be heavy but if you carry it incorrectly it can cause a problem.
Hope you're feeling better.