For each, their story raises questions: Is heaven real? What does it feel like to die?

And for each, their answer -- airing Sunday on CNN's "To Heaven and Back" -- will be grounded in their experience. These are their accounts:

MARY NEAL

It was January 14, 1999, and Mary Neal, an orthopedic surgeon from Jackson Hole, Wyoming, had surprised her husband, Bill, with a week-long kayaking trip with friends in the Los Rios Region of Chile.

It had been a good trip. The couple spent the week enjoying people, the food and the culture.

But that morning, Neal's husband wasn't feeling well. So he stayed behind while she joined their friends on a section of river well known for its waterfalls and drops of 10 to 15 feet.

"When I first put (afloat) on the river, I didn't feel quite right," she said.

Neal crested at the top of the first big drop in the river. She looked down into what she later described as a bottomless pit.

Then she went over.