She was over at a friend's house when "all of a sudden I was absolutely convinced that the house was on fire and it was burning down," the actress told Dr. Harold Koplewicz from the Child Mind Institute, as part of an Advertising Week 2018 panel in New York. "There was nothing in me that didn't think we were going to die," she said. "It was panic but I, of course, didn't know that. And it just kept going for the next two years." Therapy — and later improv and acting — eventually helped Stone manage her anxiety in the years after her disorder first emerged. But she admitted that she still struggles. "I panicked this morning, y'all," she said, with a nervous laugh. "I wasn't expecting to, but I definitely did." Stone, who recently starred in Netflix's "Maniac," first opened up about her anxiety to friend Jennifer Lawrence in a cover story for Elle magazine. Stone told Koplewicz, president of the Child Mind Institute, a nonprofit dedicated to helping children and families struggling with mental health and learning disorders, that her motivation for speaking in detail about her struggle was a desire to help others. According to Koplewicz, one in five American children have a mental health disorder, anxiety being the most common. "If I can do anything to say, 'Hey, I get it and I'm there with you and you can still get out there and achieve dreams and form really great relationships and connections,' I hope I'm able to do that," said Stone, who manages her disorder with therapy and meditation.Stone believes she also benefits from the open conversation, which she admitted "is really scary for me but very healing."Talking about her anxiety helps her "own it and realize that this is something that is part of me but it's not who I am," she added.