The book titled Proof of Heaven: A Neurosurgeon's Journey into the Afterlife is written by Dr. Eben Alexander III, could be categorized as non fiction for both science and spiritual. This book is about the doctor's experience during five days coma. As told, during coma he met angelic being who guided him on the journey where he has the opportunity to speak with the "Divine source of the universe" or the God.

The author of this book explains that his journey was not a fantasy. It is real. Furthermore, he explains that neuroscience has made him difficult to accept any belief in heaven, God, or the soul. But the journey gave him outstanding experience. It has change his life.
Here are some reviews about the book.
“Dr. Eben Alexander’s near-death experience is the most astounding I have heard in more than four decades of studying this phenomenon. [He] is living proof of an afterlife.” (Raymond A. Moody, M.D., Ph.D., author of Life After Life )
“Eben Alexander brings a unique perspective to the sacred world combining a glorious, personal vision of spiritual consciousness with patient, insightful scientific inquiry. Proof of Heaven is a compelling story of what may lie ahead for all of us in the life beyond this one. We have nothing to fear.” —Allan J. Hamilton, MD, FACS, author of The Scalpel and the Soul and Zen Mind, Zen Horse
“I can highly recommend this important book that has the potential to break many scientific taboos.” —Dr. Pim van Lommel, cardiologist, author of Consciousness Beyond Life: The Science of the Near-Death Experience
“Proof of Heaven is more than just an awe-inspiring account of a profound encounter with spiritual reality. Dr. Alexander’s neuroscience career taught him that near-death experiences are brain-based illusions, and yet his personal experience left him dumbstruck. His honest struggle to make sense of this unforgettable journey is a gripping story, unique in the literature of spiritual experiences, that may well change how we understand our role in the universe.” —Bruce Greyson, MD, co-editor of The Handbook of Near-Death Experiences: Thirty Years of Investigation
Price: $8.84 

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