Thank you again for a full and informative history.
"massage of the lower back around L13 and L14 and below."
That I am sure is just a mistype as you really mean L3 and L4 (easily done)
In direct answer to your question, the exacerbation of symptoms following massage for "skeletal issues" is surprisingly common and is, in my opinion, the rule rather than the exception......put simply massage often makes things worse initially and this can be apparent in the first few days following treatment. Thankfully it is usually temporary.
The chest problem seems muscular rather than nerve entrapment as the mid thoracic area is not that a common site for disc or nerve problems.
Monitor the situation with the normal dose of Ibuprofen ( my normal dose ;-).
Widening the post, i am glad that all the investigations have proven to be within normal limits.
It is now a matter of "waiting and seeing" hoping that it will not develop into a psychosomatic situation so common in modern folk, particularly girls, in these modern times.