Considering the seemingly relative nature of time, and the ability of the brain/mind to experience things like dreams, that may last for days in the dream, but only minutes to an awake observer..
That it stands to reason- any experience of existence after death- may simply be the brief moment in time before your brain effectively shuts down- and in that brief moment, you live out an entire afterlife.. This afterlife could last seemingly forever, and yet from an outside observer, it only be the few short moments before brain death..
Consider...
What makes this Experience any more real or unreal then that Dream?