I was talking to the director of a funeral home in Norfolk, VA.
I sort of casually asked if they ever had any wake up. He replied that they had one just the week before. They called an ambulance and took him to the hospital.
It does make you realize that they are not as perfect as some of them claim at determining when a person is brain dead or just dead at all.
This is why embalming became required for burials. Nobody waking up in a coffin and dying after days of terror.