Near Death Experiences

I have always been intrigued by any and all things unexplainable. One of those being Near-Death experiences. I have never experienced one myself but, most people report having some sort of vision, an extreme sense of peacefulness, or traveling through a tunnel that merges with light. Some even say they experienced reuniting with a loved one that has already passed on. There are skeptics that believe these experiences are simply hallucinations due to the brain being traumatized. What is the truth behind these Near-Death experiences? Are they glimpses into another realm, or are they just a medical condition? What do you think?