Neck Stiffness

I'm a 53 year old male in good health.  For the past few years, I've noticed that my neck gets quite stiff when I'm stressed.  But now I'm starting to wonder which is coming first: is stress causing the stiffness or is the stiffness causing me stress?  I can't seem to move my head at all during these moments to the left, but I can move it to the right.  Some friends have told me it may be a pinched nerve and others have said it's just anxiety related.  Are there ways of definitively detecting why this seems to only effect my neck and why it doesn't occur all the time (if it is a pinched nerve)?  What would you recommend be my next step and any suggestions I might offer my primary physician?  

Thanks!  Jimbo1956