There are many examples throughout history of people being pronounced dead, who have later bounced back to life.
There are also examples of unearthed coffins, which have scratches under the lid, implying that the buried person came back to life and furiously tried to get out of the coffin.
It's often referred to as the 'Lazarus syndrome'.
Here's a description of the Lazarus syndrome, from wikipedia.
"Lazarus syndrome (the Lazarus heart), also known as autoresuscitation after failed cardiopulmonary resuscitation, is the spontaneous return of a normal cardiac rhythm after failed attempts at resuscitation. It is also used to refer to the spontaneous return of cardiac activity after the patient has been pronounced dead. The phenomenon was first described in medical journals in 1982, and has been noted at least 38 times since then. It was named the "Lazarus Phenomenon" by Jack G. Bray in 1993, referring to Lazarus of Bethany who, according to the New Testament, was raised from the dead by Jesus."