But the condition is rarely life-threatening, and the 39-year-old Grammy winner is exercising regularly under medical supervision.

"My nervous system shut down, you know," Elliott said in an episode of the VH1 show "Behind the Music" airing June 29 on the cable network.

"Your skin is dry, your hair falls out, you wake up, your eyes feel like they've got rocks in them," she said.

Graves disease cannot be cured, but its symptoms can be handled with treatment, according to medical organization the Mayo Clinic.

Elliott, who is known for the hit songs "Get Ur Freak On" and "Work It," was diagnosed with Graves disease in 2008 but kept her condition private, her publicist Anne Kristoff told Reuters Thursday.

She said Elliott "pretty much exercises every day, so she's committed to her health."

Patients with Graves disease have a thyroid gland that overproduces the hormone thyroxine, which increases the metabolic rate and can affect a person's appearance and energy level.

Elliott gained fame in the 1990s and won four Grammys, but has not released an album since 2005's "The Cookbook." She is working on an album tentatively titled "Block Party," with producer and rapper Timbaland.

Copyright Reuters, 2011