The same thing happened to me and my Pfaff CS not too long ago. I was really puzzled. At first it started just giving me the message about my machine needing to rest, and then when it would come back on it was sewing real slow. Turns out I had a spool of thread that had somehow got wrapped around the hand wheel. It was a horrid mess and it probably took me an hour to get it all cleaned out of there, but it is working fine now. Hope yours is an easy fix.