Sounds to me like your black worms from the LFS were bad. If the worms are dirty they have a high bacteria count which can be transferred to your discus. I tried black worms from the LFS once and my fish were skittish, huddled, bouncing of the walls and acting extremely weird- I will never feed black worms again! My fish thrive and are extremely healthy without them. Just my experience....
however, I have a good friend who buys them through the mail from http://aquaticfoods.com/worms.html and she swears by them! She bought the containers and cleans them every night and her fish do great!