Sarah Jessica Parker is back on the big screen.

This time, however, New York City is merely a backdrop for her powerful performance as a singer who has to come to grips with a grim, life-changing medical diagnosis.

"I was very worried about the emotional life [because] there's so much internalized," Parker said Friday on "Good Morning America" about her role as Vivienne in "Here and Now." "It's about a singer in New York who had a modestly successful career and at the beginning of the movie is diagnosed with a glioblastoma."

The film follows the next 24 hours of her character's life after the diagnosis, which Parker called "a reckoning."

"Someone as a ghost in their own life. Recognizing regret, disappointment, attempts at fixing mistakes and trying to love correctly with the time that she has left," Parker said.

The actress, 53, said playing such a lonely character seemed "scary" at first but she was actually "shocked at how accessible all of it was."

"We had a director that created an environment where everybody felt just really relaxed and comfortable," she said.

Parker said she lost a person "very dear" to her from glioblastoma, the same diagnosis that Sen. John McCain died of the week Parker said they started filming this movie.

"It doesn't require a lot to feel the terror, the devastation, the enormous sense of having no ballast when you hear that kind of news. I can't imagine, of course, but I tried," she said.

The actress made her Broadway debut at the age of 11 in the 1976 revival of "The Innocents" and famously played "Annie" from 1979-1981.

Parker hinted that she may soon return to the stage.

"I'm thinking there might be something coming," she said.

"Here and Now" is now in theaters.