I sit on a three leg stool when I sew. This keeps my back straight and all the weight is distributed evenly. If I get out of position, the stool will tip. Never jut your neck out, or lean in to the sewing machine. Sit straight, nod your head down and keep your hands 90 degrees to the sewing bed. I had a PT come to my house to show me the correct way to sit and sew. I can sew all day and not have any pains.