Dr. Brian Weiss, Past-Life Regression Expert, Shares His Theory On What Happens When We Die (VIDEO)

What Happens When We Die? A Past-Life Regression Expert's Theory

Psychiatrist Dr. Brian Weiss didn't believe in souls and reincarnation until one patient's astonishing hypnotherapy session in the 1980s shook him to his core. Her name was Catherine, and she suffered from paralyzing phobias. Under hypnosis, Dr. Weiss asked Catherine to go back to the time those phobias started, and she did -- 4,000 years.

He didn't believe in past-life regression at first, but after Catherine's symptoms began disappearing, Dr. Weiss accepted that there may be something deeper at hand. Then, during another hypnotherapy session, Catherine relayed intimate details to Dr. Weiss about his own life. From that moment on, Dr. Weiss was a believer.

Before meeting Catherine, Dr. Weiss had always described himself as an agnostic. "When I say 'agnostic,' it was like, I don't know that I believe in God, even," he tells Oprah during his appearance on a "Super Soul Sunday" episode. "I'm aware of it and it could be, I'm just not sure. I [needed] more proof, more evidence. And I got that."

Now, Dr. Weiss has a clear opinion of the afterlife, telling Oprah that the soul is the part of us that goes on after we have died. It goes in and out of physical form, as Catherine's experience -- and many others since -- have shown him.

"We never die, because we're never really born. We existed before. You existed before this birth," Dr. Weiss tells Oprah. "You were probably a spiritual guide to your mother or someone else. You were on the other side, then you come into a physical body as a baby."

The next stage, Dr. Weiss explains, is leaving the body. "If you are the soul, you never die," he says. "When the body dies, you go on."

"Super Soul Sunday" airs Sundays at 11 a.m. ET on OWN.