Lupus Myelitis, a rare autoimmune disease, was the diagnosis for former "3rd Rock From The Sun" and current "The Exes" star Kristen Johnston.

The 46-year-old reality TV star shared on her Facebook page earlier that she suffered from the disease's symptoms for four excruciating months and visited 17 doctors before Daniel Wallace, a Los Angeles physician shed light on her disease on Monday.

The actress said at first that she was diagnosed with an undisclosed rare autoimmune disease and it was only later that she said it was Lupus Myelitis in a Facebook post later in Wednesday.

"I'm not on my death bead...far from it.I'm gonna be fine," Johnston shared concerning her ailment. "I just wanted to have a few weeks of privacy to navigate it & receive treatment."

What is Lupus Myelitis exactly? Lupus is a disease wherein an individual's immune system destroys cells in the person's own body. According to "The Lupus Book: A Guide for Patients and Their Families" by Wallace, Lupus Myelitis is described as a "rare but serious complication of lupus." Symptoms of the disease include weakness in the limbs resulting from inflammation surrounding the spinal cord or blood clots which form in the spinal arteries.

Treatment for this disease mainly centers on steroids and other anti-clotting drugs.

Johnston shared that she had previously been "really, really sick" since September.

The actress explained that she experienced full body weakness to the point that even walking was too difficult and climbing the stairs had been impossible. 

"Lying down I'm fine, which is great for writing or killing time on social media (thank you all!!), but it's kind of disastrous when you're in a sitcom that requires tons of physical comedy," Johnston dished on her current condition.

Because of Lupus Myelitis, Johnston tried to wrap up shooting for "The Exes" as early as she possibly could but still had to miss two episodes. 

She is currently receiving treatment and is ready to get back to work as soon as possible.