Rapper Missy Elliott has announced that she's suffering from Graves' disease -- an incurable autoimmune disease that affects the thyroid. (It's the leading cause of hyperthyroidism, a condition in which the thyroid gland produces excessive hormones.) In an interview with People Magazine, the 39-year-old rappers said she was diagnosed with the disease three years ago and her symptoms include hair loss, dizzy spells, mood swings, nervousness, tremors, weight loss and excessive sweating. "I was [driving and] trying to put my foot on the brake, but my leg was jumping," she says. "I couldn't keep the brake down and almost crashed. I couldn't write because my nervous system was so bad -- I couldn't even use a pen." Doctors are unclear as to what exactly causes the disease, but Missy, who has been off medication for a year, has been managing the disease through radiation treatment, a change in diet and exercise.