If I’m not mistaken death used to be defined at “the heart stopped beating, (s)he’s dead,” and sometimes people woke up in graves because they were not actually dead…
That’s where the expression saved by the bell comes from IIRC. Rich people were able to have a string in their grave which they could pull in order to ring a bell if they woke up in their grave, and somebody would come and dig them up.
Everything past that is just superstition and belief in supernatural at this point.