I believe that when someone is in a coma or near-death experiance, (reference: BBC, The Brain with David Eagleman, What is reality?) comes from the fact that the brain is still active, and like on Alcatraz where in the 'hole' they created their own vivid reality, the same thing happens. So when they claim to have gone to heaven, they have gone to heaven in their mind, and not a real, physical place. Although saying that, it's no less important to them than the Earth we believe we are in. Colour, smell and sounds don't exist outside our mind, but yet they still hold importance to us. But when we die, well, we're brain dead. Or are we? ... nobody can ever return to tell us. Unless ghosts are real, then they could tell us. But we have a freedom of opinion unless it's hurting someone [UK], and I don't see how an individual's belief that afterlife exists can hurt another individual, unless they're forcing another to believe in an afterlife.