I was flatlined in 1980. I somehow did an auto-resuscitation with nobody else around while I was in hospital being treated for incipient septicemia. The antibiotic put my heart into Torsades de Points and then it all stopped.
I have no idea how long I was fully out but if nothing else I was just a few seconds away from death. In medical records of over 1000 people in 16 countries there are no cases of somebody doing a full auto-resuscitation without medical assistance in a case like mine without suffering severe brain pathology.
Time to get back to work. I put in about eight hours a day.