Jamie-Lynn Sigler has been battling multiple sclerosis (MS) for 15 years.
The former 'Sopranos' star was diagnosed with the neurological condition when she was just 20 years old but still finds it "hard to accept".
Speaking of opening up about the condition, she said: "I wasn't ready until now.
"You'd think that after all these years, somebody would be settled with something like this, but it's still hard to accept."
The 34-year-old star was symptom-free "for quite some time" but has got progressively worse over the last decade.
She told People magazine: "I can't walk for a long period of time without resting. I cannot run. No superhero roles for me.
"Stairs? I can do them but they're not the easiest. When I walk, I have to think about every single step, which is annoying and frustrating."
Jamie-Lynn has tried a number of medications for the condition - which has no cure and affects the central nervous system - and her symptoms have been stable for the past six years thanks to taking a pill named Tecfidera twice a day.
She said: "Things are manageable now. It takes a fighting attitude to deal with all this. This disease can absolutely take over your life if you let it."
Though the actress - who has a two-year-old son, Beau, with new husband Cutter Dykstra - doesn't know what the future holds, she is feeling "excited".
She said: "I don't know what's to come. But I'm excited for the first time in a long time.
"I've got my brain and my heart and I've prepared myself for everything that could happen. But I've got an amazing husband, the best son, and I hope that we can make more babies and just keep having fun. I'm the luckiest girl in the world."