I think I recall one other poster many years ago , that woke up with instant problems, can't recall their user name though, it may have been on a another forum, long time ago.

Did you get to see the x rays or the results yet?
One of the first steps is to rule out any cervical spine or shoulder issues, also to check for extra cervical rib or anomalies.

Some quick thoughts-
hyper mobile?
previous injury to head, neck, shoulder? - whiplash, falls, sports - whole life? These can be a factor in creating scar tissue, adhesions, restrictions and as we age the effects tend to show up more, esp if we have done repetitious or other aggravating activities. IMO

This site has some positional testing images that may help to determine if more in depth TOS testing should be done.
images in the middle of the page -
http://www.nismat.org/ptcor/thoracic_outlet/

Personally some of the stretches they show are too extreme for many of us w/TOS unless done very slowly and gently.
mine is mild most of the time now & I could only do those if I was really warmed up and did a good cool down and didn't force any part of the stretch. If I stretched as much as I could , then I'd have delayed pain hrs to days later. I much prefer Sharon Butler stretches & suggestions.


In the sticky post #1, definitely check out the info on trigger points, Sharon Butler's book or website (info on fascia restrictions as a cause)
there's just tons of info in the whole thread too.
http://neurotalk.psychcentral.com/thread84.html