For a piece of meat we tend to overcomplicate things.) I bet it's some sort of hallucinations while your brain cells die of suffocation, and then *click* - lights out. Or even no hallucinations - when you fall asleep, the quick sleep phase (REM phase, when\where you experience dreams) is the last one, so your brain won't live that long to experience it.
I'd even put it that way - when you die (finally lose your consciousness due to any reason), it's like falling asleep, but you go like 5 minutes into it, before your brain cells die out.