The 'Get Ur Freak On' singer stated that the symptoms of the condition - which can include shortness of breath, increased sweating and restlessness - came over her suddenly in 2008, according to People.
"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," Elliott said. "I couldn't write because my nervous system was so bad - I couldn't even use a pen."
The 39-year-old went on to reveal that she has been undergoing treatment for the disease, in which an overactive thyroid causes a metabolic imbalance of thyroid hormones in the body.
"I'm 30 pounds lighter because I've been exercising," Elliott said. "My thyroid is functioning, so I haven't had to take medication in about nine months. [But] you live with it for the rest of your life."
The rapper said in October of last year that she is planning a comeback, stating that she is at work on a new LP.
Elliott revealed in August 2010 that she still thinks about Aaliyah "every day", claiming that the late singer is an inspiration to younger artists.