Christina Applegate thought she was living with multiple sclerosis (MS) for five years, until recently discovering she had been given a wrong diagnosis.
The actress, known for hits like Anchorman and Married With Children, said she was "not happy at all" about the news and in tears when she found out.
"You don't get misdiagnosed and then all of the sudden I'm better," Applegate said in an episode of her Messy podcast released on Tuesday. "If anything, I've gotten worse."
The two-part episode, co-hosted by Jamie Sigler, ends a recent break she took to process the information. An investigation into what is causing her debilitating symptoms - which she experiences daily - will begin next week.
"I'm back at square one where I don't know what's going on with me," she said.
In the podcast, Applegate said that "all of a sudden, a few years ago", her doctor suggested ending her infusion treatment for MS to see how her body reacted.
During the time off, her body did not respond in a way that would indicate she had MS.
Doctors then looked into her case further and concluded she in fact did not have the autoimmune disease, which can cause muscle stiffness and problems with walking and talking.
"She came into my room and said, 'Congratulations, you don't have MS,' " Applegate said, recalling the moment.
"I was, like, not happy at all," she continued. "Everybody else was so happy."