Missy Elliot performs at Lilith Fair in 1998. (Shawn Thew)

Elliott told People magazine the illness had made even simple, day-to-day tasks difficult for her. “I couldn’t write because my nervous system was so bad – I couldn’t even use a pen,” she said.

The ominously named disease is unfamiliar to most people. We explain what you need to know about Graves’ Disease below.

What causes Graves’ Disease?

Graves’ Disease happens when too much thyroid hormone is produced, a condition called hyperthyroidism, according to the Mayo Clinic. This higher thyroxine level can greatly increase your body's metabolic rate, which may affect weight, mood, and energy.

What are the symptoms?

The symptoms aren’t pretty: rapid heart rate, tremors, double vision, insomnia, fatigue, muscle weakness, anxiety, and in men, enlarged breasts. The list goes on. Elliott, 39, says she’s suffered hair loss, mood swings, and muscle control loss since she was diagnosed with the condition three years ago.

How can it be treated?

Elliot says radiation therapy and time at the gym has helped her get better. Other treatments include anti-thyroid medications and doses of radioactive iodine to shrink the gland. If left untreated, Graves’ Disease gets worse over time. But, if diagnosed properly like Elliott’s was, a person can continue to live a mostly normal life. Elliott is now reuniting with Timbaland for several new songs, and her much-awaited seventh album, Block Party, is on its way.

President George H.W. Bush and First Lady Barbara Bush also suffered from Graves’ Disease. Read about how it affected their lives here.