When I was at Uni this kind of thing was the focus of my dissertation and I find it absolutely fascinating:
In April, 1962, [Clairvius Narcisse] checked himself into hospital in the town of Deschapelle in Haiti. [He] had been sick for some time, complaining of fever, body aches, and general malaise, but recently had begun coughing up blood. His condition deteriorated rapidly. Physicians noted that Narcisse suffered from digestive disorders, pulmonary edema, hypothermia, respiratory difficulties, and hypotension … his lips turned blue [and] he reported tingling sensations all over his body. Two days later his two attending physicians, one of whom was American and the other American-trained, pronounced Narcisse dead and he was buried the next day.
Eighteen years later, [his sister] was walking through the village marketplace when she was approached by someone claiming to be Clairvius Narcisse. The man identified himself by a boyhood nickname which which was known only to members of the immediate family, and he had a bizarre tale to tell…
He said that as he was pronounced dead he felt as if his skin was on fire, with insects crawling beneath it. He heard his sister Angelina weeping and felt the sheet being pulled up over his face. Although he was unable to move or speak, he remained lucid and aware the entire time, even as his coffin was nailed shut and buried. He even had a scar which he claimed was sustained as one of the coffin nails was driven through his face. There he remained, for how long he did not know, until the coffin as opened by the bokor (sorcerer) and his henchmen. He was beaten into submission, bound, gagged, and spirited away to a sugar plantation that was to be his home for the next two years.
On the plantation, Narcisse and other zombies labored from sunup to sunset, pausing for only one meal a day. He would later report that he passed his time there in a dream-like state, devoid of will or volition, with events unfolding before him as if in slow motion. They were given a paste made from datura which at certain doses has a hallucinogenic effect and can cause memory loss. When the boker was killed, and the regular doses of the hallucinogen stopped, the slaves were able to regain their senses and escape.
Two scientists investigating Narcisse’s claims have concluded that Narcisse was initially poisoned by a dose of a chemical mixture containing tetrodotoxin (pufferfish venom) and bufotoxin (toad venom) to induce a coma which mimicked the appearance of death. The instigator of the poisoning was thought to be Narcisse’s brother, with whom he had quarrelled over land. Upon returning to his village after the death of his brother Narcisse was immediately recognised. When he told the story of how he was dug up from his grave and enslaved, the villagers were surprised, but accepted his story because they believed that his experience was a result of voodoo magic.
[Sources: Much more detailed article here : Wikipedia]