You might want to explore our Thoracic outlet syndrome forum (TOS for short)
*Especially if repetitive work or previous whiplash or such has occurred.*
http://neurotalk.psychcentral.com/forum24.html
and the TOS useful sticky thread-
http://neurotalk.psychcentral.com/thread84.html
(start with post #1 it is a beginner crash course for TOS info w/ links)