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As I see it you sure woke up on wrong side of the bed the other day. It seems a slight spasm of your muscles must have caused the initial discomfort, which due to lack of proper rest must have aggravated. There also seems to be a neurological component unless you dont have tingling
or pin pricking or burning parasthesias in the distal part of forearm and hand. Having said that I suggest you stop using a pillow for some time (or use a really thin one), give a nice hot fomentation to the neck and arm, avoid the aggravating activities like lifting heavy objects, and lastly take frequent stretch breaks at work. If it still persists..I'll tell you some investigations, the reports of which you can mail me at firstname.lastname@example.org
Have a good one