I have had that happen too. Empty bobbin also. I will think the bobbin is close to running out and check it often, of course I keep sewing and think it will last until I'm done. You guessed it, after sewing a long seam, as in a border. Go to cut the thread and yep, I ran out not long after I started. I just put in a new bobin and redo it. Getting angry is a waste of time, it would happen too often with all I the ways I can screw up.