There's actually a really interesting theory on death that I want to say was founded at the University of New Mexico(I'd have to check my sources) that has to do with dimethyltryptamine (or, DMT). Basically, DMT is a naturally occurring tryptamine and neurotransmitter. Just about every living thing produces it, and at the same time, it is the most powerful hallucinogenic substance known to man. It's more illegal than heroin, yet we can extract it from grass, tree-frogs, and even the human brain. DMT is only released during two processes... sleep, and death. When you dream, you're actually experiencing a similar experience to the psychedelic/hallucinogenic effects of DMT.
So, the theory hypothesizes that when you die, your brain releases every last drop of DMT. Now, it takes a very, very miniscule ammount to create dreams or to achieve a psychedelic experience in recreational use. We're talking micrograms. Imagine a dose millions of times larger. It's commonly theorized that you have approximately 12 seconds of brain activity after death, and it is also a well known fact among the drug culture that any psychedelic substance is going to alter your perception of time.
Here's where it gets interesting: basically, what this hypothesis states is that those 12 seconds of brain activity, due to the unbelievable strength of the large amounts of DMT being released, seem like an eternity. So, in summary, imagine a psychedelic trip that lasts an eternity, and you've got it. And if that's so, why fear death at all? Why fear it if, in retrospect, it is a euphoric experience. I'm not saying this is what happens when you die... I don't think anyone can rightfully say they know what comes after life, but this is certainly an interesting theory.
Some scientists use this possibility to explain the "near death experience"... You know... Seeing the light and all that.
But my question is, what if you die in your sleep? Are you stuck in that dream for that 12 second eternity? What if you die in the middle of a nightmare? Is that hell?
Again, I'm not saying this is what happens when you die, and I have a feeling I'll get some skeptical responses from some of the more religious posters here if I don't say so, but it certainly is interesting.
I actually wrote a short story based around the theory.