I, too, have suffered from panic/anxiety/PTSD for the past 5 1/2 years and have the pain in
my breast and under
my arm. Often I have tingling down my arms or the muscles in
my biceps will tighten up and cause pain.
I believe, from working with a panic disorder specialist, that this is the cause of an over abundance of adrenalin. The fear of fear is what causes our panic/anxiety attacks and that, I feel, is what causes the pain.
But, that doesn't make it any less real or painless!