Does it only happen at night and only in your sewing room? Does it happen aftering you've been standing for some time? I get what feels like very light electrical shocks in my legs when I've worked out (on treadmill with an incline or the elliptical) a little longer or have been standing on a hard surface for some time. Also is your sewing machine sitting on front of a window that could be attracting very tiny insects that can get thru a closed window?