If you hunch over while sewing it is very likely that you hunch over at the computer, while walking, pushing the grocery cart (you know, resting your arms on the cart and gliding along). My physical therapist helped me to change the hunch over habit and it has really made a difference. Just being aware of it and pulling myself upright as I walk has helped with a number of walking issues I had.
I spend 8 hours a day at a computer and changing my workspace (including a decent chair) made a great deal of difference. I am still working on my sewing set up but don't have the right combination yet. So i stop quite often, pull myslef upright and walk around a bit.