(NBC News) - The near-death experience may be as close as humans get to glimpsing something out of this world.

It seems to happen to some people when their heart stops and they're flat-lining. Once revived, they remember floating above their body. They believe they reconnected with deceased loved-one or they say they suddenly understand the meaning of life. The accounts are remarkable and widespread, transcending age, language, culture and geography.

But is the experience imaginary or a true glimpse into the afterlife? TODAY's Natalie Morales is taking a closer look as part of our two-day series "Do you believe?"

The International Association For Near Death Studies — a large organization dedicated to research, support, and education of the phenomenon — estimates more than 15 million Americans may have had a near-death experience.

Barbara Bartolome says she’s one of them.

At 31, she went to the hospital for a myelogram, a diagnostic imaging procedure that involves injecting iodine dye into the base of a patient’s neck.

Bartolome said the dye accidentally went into her brain and within moments, she was unconscious and flat-lining.

“I literally went from inside my body, and when I shut my eyes… the next second I was up on the ceiling looking down at the entire room,” she recalled.

“There was this feeling of a presence that was next to me. It felt like it was God. It felt so loving and so accepting, and so eternal. I literally looked down and said, ‘Huh, if I'm up here, and my body's down there, then I think I must have just died.’”