THE Big Yellow Taxi singer, 70, has been battling a bizarre medical nightmare known as Morgellons disease. Though the ailment is sometimes diagnosed as a "delusion of parasites" and patients are sent to psychiatrists, Joni Mitchell insists her sickness is real. "I have this weird, incurable disease that seems like it's from outer space," she says. "Fibers in a variety of colors protrude out of my skin like mushrooms after a rainstorm. They cannot be forensically identified as animal, vegetable or mineral." She released her last album of new songs in 2007, then retired. Apart from traveling to Toronto in her native Canada to attend a special tribute to her music, she has spent much of the last 10 years inside her Los Angeles home. "You can call me a recluse," she says. "But I like living alone."