Death: The irreversible cessation of all vital bodily functions.
However, it is theorized that after death, the brain remains in a comotose state for a few minutes.
now, if being in a coma is almost identical to sleep (aka, unconsiousness) then that means that DMT should be released into the individual.
DMT basically causes dreams. now, while the brain panicks and grasps for oxygen (which is impossible seeing that breathing has stopped) you are dreaming while you fully shut down. Is this dream "Heaven?"