I received an email at work one day that was talking about "stare-ing" at the computer screen all day in the same position. As you scrolled down thru the email the "text" would change directions - first printed straight on - then would change sideways to the left and then sideways to the right and back and forth. So the entire time you are reading the email you were physically bending your head/neck to one side or the other to read it.
THUS.... you were excerising your neck mucsles without really realizing it! Until you realize that that little movement really did feel good! Even simple things like that can help avoid "stiff necks" when sewing. Same with shoulders just stop and roll your shoulders up, down and around every so often. I know I have to make myself relax my arms and shoulders when doing FMQ. I get so caught up in it and then realize I have tensed up my hands, arms, shoulders and neck. I have to stop, stretch and then begin again the concentrate on R E L A X I N G while quilting. Easier said than done!