Missy Elliott Reveals Mystery Ailment

In an upcoming episode of VH1's "Behind The Music", reveals the reason she's been keeping a low profile lately.

Elliott revealed to The Hollywood Reporter that she has been battling Graves' disease, an autoimmune disorder that affects the thyroid. In an upcoming issue of People,  she admitted she's had the disease since 2008.

According to Elliott, I was [driving and] trying to put my foot on the brake, but my leg was jumping. 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."

Elliott's episode of  "Behind The  Music" will air Wednesday, June 29 at 10/9pm central on VH1.