From 2013 to 2015, two villages in northern Kazakhstan began to suffer from the same, strange affliction known as "sleepy hollow".
Over these years, villagers began to suffer from bouts of "death-like" sleep that could last for days or even weeks. The episodes could start while residents were at home, in bed, or even while walking around. While they were asleep, they would sometimes walk around and even appear to be conscious, but then begin to snore, and remember nothing upon awakening of the hours or days they spent in this state.
For some, the illness was more serious. Sufferers experienced strokes, or else strange hallucinations. Children told Komsomolskaya Pravda they had seen winged horses, snakes crawling in their beds, worms eating their hands, and their mother suddenly having eight eyes.
For several years, the mystery remained unsolved. Nearby uranium mines which had been closed shortly after the fall of the Soviet Union were another source of suspicions, though mass testing of homes didn't find significant levels of radiation.
Some thought that tainted alcohol could be a cause of the illness, or even a type of mass hysteria, but that didn't stand up to much scrutiny. Every age group was affected by the illness, with some victims suffering several bouts, as well as other symptoms such as waking memory lapses and severe headaches. Even a cat called Marquis was affected.
"He seemed to be foolish, throwing himself against the walls, cabinets, meowing," Elena Zhavoronkova told Time.kz in 2015. "He tortured us until three in the morning. They took him out to the veranda, where there was a dog, so the Marquis began to rush at it."
"Then he fell asleep in the morning and snored like a man until Saturday afternoon. He did not react to anything, not even to cat food. And when he came to, he was lethargic, could not even jump on a chair."
Cats are not known for their susceptibility to mass hysteria, nor their love of counterfeit vodka.
In the end, the problem turned out to be that the villagers' brains were being deprived of oxygen. The cause was attributed to the uranium mines, but not through radiation poisoning.
"The uranium mines were closed at some point, and at times a concentration of carbon monoxide occurs there," Deputy Prime Minister Berdibek Saparbaev said in July 2015. "The oxygen in the air is reduced accordingly, which is the real reason for the sleeping sickness in these villages."
Carbon monoxide binds to hemoglobin and forms carboxyhemoglobin – binding much more effectively than oxygen, which leads to a much lower supply of oxygen to the brain. Having isolated the problem, the government immediately began evacuating residents.
By the time the cause was found, up to a quarter of the villages' inhabitants had come down with the illness.