After knocking out six classic or near-classic albums between 1997 and 2005, Missy Elliott's madcap pace came to a screeching halt. A few scattered tracks and 10 years later, Elliott is primed for a comeback, hot off her spot with Katy Perry and the Super Bowl halftime show and with a knockout Pharrell collaboration "WTF" out now.

But what kept the boundary-pushing rapper/producer out of the game for so long? In Elliott's new Billboard cover story, she talks about how Graves' disease -- which she was first diagnosed with after losing an extreme amount of weight in 2008 -- affected her body and her life. "It causes hair loss, your eyes bulge,” Elliott says. “My blood pressure was always up from just overworking.”

Billboard Cover: Missy Elliott on Her Comeback -- 'There Is Only One Missy'

Not familiar with Graves' disease? Many aren't. Here's a primer on the immune system disorder Elliott suffers from, information courtesy of Mayo Clinic.

Symptoms Include: Weight loss despite normal eating habits, anxiety, frequent bowel movements, hand tremors, bulging eyes, heart palpitations.

Causes: An overproduction of thyroid hormones, although specialists aren't sure why this starts in previously healthy individuals.

Who Is At Risk? Primarily women, people under 40, smokers, those under a great deal of stress and people with other immune disorders.

Treatment: Anti-thyroid medication, radioactive iodine by mouth and even surgery are used to deal with Graves'.

What Sufferers Can Do: Exercise, eat well, avoid stress.

In the Billboard cover story, Elliott's protege and close friend, rapper-dancer Sharaya J, saw first-hand the effects of the disease on the hip-hop star when she first began working with her around the time of her diagnosis. “It started to change her way of life,” she says. “There were physical changes, extreme headaches, extreme weight loss. What that does to a person, being a public figure and knowing people are looking, judging? That’s a tough thing.”

Missy Elliott: The Billboard Cover Shoot

Now, with the help of medication, Elliott has gotten her condition under control. To read more about Elliott's health struggles and her return to the spotlight, read the full Billboard cover story here.