when you die, it is usually your heart that gave up on you, but you brain is still working for 5 minutes or so, and then your brain cells start to die due to lack of oxygen.

so when you think about it, even if people see you dead - laying there on the floor, you're really still alive for next 5 minutes, you hear stuff and smell things.

i don't know if it is true, because nobody ever went back...
it is just my theory