The actress -- who first shared her MS diagnosis in 2021 -- revealed on Dax Shepard's "Armchair Expert" podcast that she now has 30 lesions on her brain, the largest of which is behind her right eye. She says it's causing so much pain, she describes it as "the worst thing that's ever happened to me in my entire life. I hate it so much, and I'm so mad about it."

Thankfully, the lesion has yet to impact her vision. She has felt other MS side effects, however, as her mobility's been greatly affected.

She added, "My hand starts to go weird and then I’ll get a seizure-y feeling sometimes in my brain."

Christina says the pain is so intense, "You can't overcome it" ... and she gets annoyed when people ask why she doesn't exercise.

Despite her struggles, she wants to speak truthfully about all of it -- and remembered not being entirely honest when she had breast cancer in 2008 ... something she says didn't help anyone, especially herself.

Still, the star hasn't lost her humor amid her health battles. Remember, Christina -- who uses a cane to walk due to her MS -- roasted the crowd at the Emmys after they gave her a standing ovation during the rare public appearance.