Between 2012 and 2015, people living in the village of Kalachi in Kazakhstan fell into slumbers lasting up to six days, suffering from 'violent hallucinations' and experiencing increased sexual desire.
Children in the area reported seeing winged horse and snakes in their beds, and one woman claimed her cat began acting 'stupid' throwing itself at the wall and attacking her dog.
Around 160 people suffered from the strange condition in the village that became known as 'Sleepy Hollow'.
A 2014 investigation by the newspaper Komsomolskaya Pravda described how it manifested itself.
The publication reported said: "The sick person appears to be conscious and can even walk. But all the same he then falls into a deep sleep and snores, and when they wake him up... the person remembers absolutely nothing."
While one woman in the village reportedly said: "As soon as men wake up, they need sex right there and then, and this feeling lasts for at least a month."
Another resident claimed: "One poor man wet himself as he went to hospital. So the paramedics removed his pants and there he was, not properly conscious but in a state of sexual excitement."
Located near a Soviet-era uranium mine, a number of theories were considered, from poisoned water and dodgy vodka to mass hysteria.
Hundreds of people from the village were relocated and the cases of spontaneous narcolepsy eventually stopped.
And in 2015, the Kazakhstan government released a statement claiming it had solved the mystery once and for all.
It claimed toxic levels of carbon monoxide was to blame.
Tests carried out found CO levels in Kalachi were 10 times higher than normal.
Speaking to the Daily Mail, Berdybek Saparbayev said: "The cause of the bizarre sleeping illness has been determined.
"After numerous medical tests, our researchers have confirmed that carbon monoxide is to blame for sleeping epidemic in Kalachi village."
Russian scientist Leonid Rikhvanov said the carbon monoxide had made its way way from the disused mines and smothered the village.
He said: "To describe it simply, when the uranium mines were abandoned, they began to fill with ground water.
"Radon and other inert gases which release as a result of the decay of uranium are squeezed out by groundwater and through the cracks in the ground rises to the surface."
However, even this has since been disputed.
Last year, Professor Byron Crape from Nazarbayev University in Kazakhstan said his research had led him to disagree with claims carbon monoxide was the root cause.
Instead he believes Kalachi's water supply had been contaminated by chemicals buried beneath the disused mines, which has seeped into the soil.
He said: "Over the course of a long-term analysis, we excluded dozens of hypotheses stating that the disease could be associated with food, chronic diseases or bad habits of the villagers.
"But then we found out that all residents of Kalachi drink water from one source - from an underground pump of a local resident who pumps it and sells it to his fellow villagers.
"Chemicals could have infiltrated drinking water through uranium mines that have been abandoned since the late 1980s."
Over 120 families remained in Kalachi, with no more incidents of the sleeping sickness having been reported.
Professor Crape says this is due to the fact barrels containing toxic chemicals have now emptied and therefore the water supply is no longer affected.
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