Credit: Michael Rozman/Warner Bros.

Three-and-a-half weeks after she and fiance Martyn LeNoble welcomed daughter Sadie Grace, first-time mom Christina Applegate opens up about the life-changing experience during a Tuesday appearance on The Ellen DeGeneres Show.

Applegate, 39, reveals that she was in labor for an arduous 18 hours -- and it was anything but painless, particularly because she had a bad reaction to her epidural.

"I didn't like it," the Hall Pass actress says. "I didn't like the feeling of numbness....It was really creepy to me. It was too much, so we turned it off and we opted to go all the way...Feeling it all."

Going without an epidural "was profound," the star explains. "It was profound pain."

And when her baby daughter finally arrived (weighing 7 lbs., 8 oz.), the breast cancer survivor surprised herself. "I dropped my gown, which I don't do," Applegate reveals. (Applegate underwent a double mastectomy in summer 2008 following her breast cancer diagnosis.)

"This part of my body is very private to me," she admits of revealing her chest in the delivery room. "That's a real private place. A place that I don't have a good relationship with, let's say."

"But at that moment of pulling [Sadie] out and I just tore that thing off. There's a room full of people that I don't know. Nurses and doctors. And she and I just laid there," Applegate says. "It was the best thing that's every happened to me."