It sounds like a scene from a horror film. Earlier last year, a tiny village in Kazakhstan was hit with a mysterious “sleeping sickness.” Residents were falling asleep at random; they were passing out while walking, in school and even on their motorcycles. Some fell asleep for up to six days at a time and when they woke up they couldn’t remember what happened. Others suffered from hallucinations, fatigue and headaches. But what was making residents in the town sporadically fall asleep?

The sleeping sickness first hit the town in March 2013. Researchers – including sleep disorder experts – who went to investigate were left stumped at what was causing the mysterious illness. Now, government officials announce that the nearby uranium mines are to blame. The mines, which were closed shortly after the fall of the Soviet Union, are thought to be the cause of heightened levels of carbon monoxide and hydrocarbons in the air.