When you sit on a sewing machine for a long time, you must maintain a good sitting posture; otherwise, it presses an extra pressure on your spine and causes pain. You can break every alternating 30-40 minutes, do some back sketches, use a good ergonomic chair, etc. Some doctor recommend to use a posture corrector belt to better posture; you can try it. One more important point when you are free from work, you also have to maintain good posture in every activities such as sitting, sleeping, walking, driving, cooking, etc. Thank you.