The Ergo Expert I saw on one of the quilt shows said never lean forward into the sewing machine. You should be looking down at the machine and have the machine tilted toward you if necessary.
Your arms should be at a 90º angle from you body, hands level with the sewing surface. At first it seemed the machine was way too low this way but it works.
You can lower you neck but never hunch forward, that causes all kinds of problems. I made myself sit very straight and only lower my head to sew and the difference is amazing. My back, neck and shoulders do not hurt at all after sitting at the machine for a long time. If you hurt after sewing you might try this way.