You've gotten a lot of good advice here!
A simple trick I learned years ago on "Simply Quilts" --- "Yes, No, Maybe So". Every 15-20 minutes, stop sewing for a minute--Nod your head about 6 times, as if you were saying "yes"; move your head from side to side about 6 times, as if you were saying "no"; shrug your shoulders about 6 times, as if you were saying "maybe so". It helps relieve neck and shoulder fatigue.