Psylly Legs is a disease that causes someone's legs to spasm rapidly and start moving around like they are dancing. The disease is generally caused by nostalgia for a simpler time. Joan previously suffered from psylly legs and began feeling it whenever she felt like her childhood is being ruined. There are two cures to the disease: either keep feeding the affected's nostalgic delusions or convince them to accept change and move on. It was named after Roberta Psylly, who was the first person to be diagnosed with the disorder. It appeared in "Saved by the Knoll".