Britain's The Independent cited local Spanish media, which reported employees at the morgue at the Legal Medicine Institute of La Corredoria heard Gonzalo Montoya Jiménez snoring from inside his body bag as they prepared to conduct his autopsy.
Gonzalo Montoya, who was convicted of theft of junk, regained consciousness just hours before an autopsy was due to be performed.
"The court sent a forensic doctor who was the one who actually confirmed his death", a spokesman from the prison department said.
Two doctors who were on duty in the prison examined the man and determined he did not show vital signs.
When Jiménez was "resurrected", the first thing he did was ask for his wife.
He was taken to the Institute of Legal Medicine in Oviedo for an autopsy.
"Relatives have been visiting him in the hospital and are said to be feeling a mix of relief and indignation, although none of them have yet made any public comment", the Sun reported.More news: Edward Snowden joins outcry against Aadhaar
Civil Guard officers answering to bosses in the northern port city of Gijon have been tasked with keeping watch on the prisoner while he is treated in hospital. This theory has yet to be confirmed by medical professionals.
He failed to show for the prison's morning count in the most unsafe section of the prison and appeared to be suffering from rigor mortis, having no pulse when found.
"The pills are taken as they (the prisoners) want".
A police source said: "We got the original call asking us to attend the jail because an inmate had died and acted according to protocol".
Montoya has been in prison for 29 years. If he goes in, he will come out as a body. Shocked by his nephew's suicide attempt, he said he nevertheless understood it.
His father José Carlos Montoya, also blamed the prison for negligence of his son's life and demanded for his release.