Revealing for the first time exactly how she felt on the afternoon of Aug. 14 when she suffered the heart attack – unknowingly at first – O'Donnell, 50, tells PEOPLE in its new issue, "My arms starting aching and my chest hurt. My son, Blake, said, 'Mommy you look very white.' I told him, 'I don't feel so good, honey.' "
The comedian didn't find out what had happened to her until the next day when she visited her doctor, who immediately put in a stent to restore blood flow.
"I started crying," O'Donnell reveals in the candid interview. "I almost died – and that's not an over-exaggeration. That's a fact."
Once back home, she threw out all her junk food and started eating healthfully. She's since lost 12 lbs. off her 200-lb.-plus frame. "For the first time, it wasn't hard for me," she says. "It took a heart attack for me to learn to take care of myself."
"I've been given a second chance," says O'Donnell, who is excited about her upcoming annual Rosie's Theater Kids Gala in New York City on Oct. 15. "I want to be there for my theater kids too. I'm getting an extra lap now. Make it worth something, kid."