The following was published on The Lancet in the year 1997. These are 3 cases of real life Zombie that the researchers observed while they are in Haiti.
FI was around 30 years old when she Died after a short febrile illness and was buried by her Family the same day in the family tomb next to her house. 3 years later she was recognised by a friend wandering near the village; her mother confirmed her identity by a facial mark, as did her 7-year-old daughter, her siblings, other villagers, her husband, and the local priest. She appeared mute and unable to feed herself. Her parents accused her husband of zombifying her (he was jealous of her after she had had an affair). After a local court authorised the opening of her tomb, which was full of stones, her parents were undecided whether to take her home and she was admitted to the psychiatric hospital in Port-au Prince [...] WD, 26 years old, was the eldest son of an alleged former tonton macoute (secret policeman) under the Duvaliers' regime. The Father was our Principal Informant together with WD's mother and other villagers. When he was 18, he suddenly became ill with a fever, "his eyes turned yellow," he "smelled bad like death," and "his Body Swelled up". Suspecting sorcery, his father asked his older brother to obtain advice from a boko [or sorcerer], but WD died after 3 days and was buried in a tomb on family land next to the house of a female cousin. The tomb was not, as was customary, watched that night. 19 months later, WD reappeared at a nearby cock fight, recognised his father, and accused his uncle of zombifying him [...] MM, aged 31, was the younger sister of our principal informant who described her as formerly a friendly but quiet and shy girl, not very bright. At the age of 18, MM had joined some friends in prayers for a neighbour who had been zombified; she herself then became ill with diarrhoea and fever, her body swelled up and she died in a few days. The family suspected revenge sorcery. After 13 years, MM had reappeared in the town market 2 months before we met her, with an account of having been kept as a zombi in a village 100 miles to the north, and having borne a child to another zombi (or perhaps to the boko). On the death of the boko, his son had released her and she travelled home on foot.
The first case (FI) is diagnosed with a catatonic schizophrenia, WD is suffering from brain damage and epilepsy presumably due to the lack of oxygen in the brain and patient MM with a foetal alcohol syndrome (FAS).