Hello,
Can you think of anything that might have set it off?
Perhaps something at work or sports activities?
Any past whiplash or upper body/head/neck injuries?
Any repetitive motion injuries in the past?
If any of those might fit you can explore our Thoracic outlet syndrome forum (TOS) for short..
here is the link to the useful sticky thread-
http://neurotalk.psychcentral.com/thread84.html