By Jennifer Arellano
Updated December 19, 2013 at 04:53 PM EST

Kristen Johnston, best known for her role on 3rd Rock From the Sun, has been diagnosed with lupus. Her symptoms from the auto-immune disease have disrupted her regular appearances on TV Land’s The Exes.

The actress announced her diagnosis through a lengthy note on her Facebook page Tuesday afternoon. “This is how, after 4 months & 17 Drs (no lie) I’ve FINALLY been diagnosed with a rare auto-immune disorder,” Johnston wrote. “Meaning my immune system has decided to go rogue and attack my muscles.”

Johnston, who plays Holly Franklin on The Exes, took a break from filming in order to complete two week-long treatments at The Mayo Clinic. She has been suffering from such chronic “full body muscle weakness” that it has made it difficult for her to walk.

But the actress assured her fans that her absence from the show won’t be for long. “The good news: I’m finally on the right treatment, feeling better & back at work!” Johnston continued. She will appear on The Exes‘ Christmas special episode Friday.

Johnston is best known for her role as Sally Solomon in 3rd Rock From the Sun and as a memorable party girl Lexi Featherston on Sex and the City.