Scientists have finally discovered why residents in a remote Kazakhstan village known as Sleepy Hollow are mysteriously falling asleep for days at a time.

They claim radon gas from nearby Soviet-era uranium mines seeped up to the surface and poisoned the residents of Kalachi.

Radon is a colourless, odourless and tasteless gas which occurs naturally through the decay of uranium and breathing it is thought to cause lung cancer.

Local government officials are considering plans to move the entire village because they feel it is impossible to eradicate radon gas from the area.

Although radiation levels in the mines themselves are not thought to be dangerous, they have left a deadly legacy for the villagers above.

'Sleepy Hollow': After four years of studies, scientists have finally discovered the cause of a mysterious illness which caused people to fall asleep for days

Radiation: Scientists say radon, which occurred naturally from uranium in nearby mines, seeped to the surface and poisoned the residents of Kalachi

Deadly: Radon - a colourless, odourless and tasteless gas - is thought to cause lung cancer and has affected around one in five people in Kalachi (pictured)

Radioactive remains: Although radiation levels in the mines themselves are not thought to be dangerous, they have left a deadly legacy for the villagers above

Professor Leonid Rikhvanov from the Department of Geo-ecology and Geo-chemistry concluded the local mines were to blame after ruling out a virus or bacteria as the cause.

He said: 'The mines left open spaces underground which were slowly filled with water that has risen upwards, driving pockets of gas inside them to the surface.

'The gas has a toxic effect that pushes a person into a dream like state, and the person then falls asleep.'

Professor Rikhavanov and Tomsk Polytechnic University have carried out thousands of experiments on the area for over four years.

They failed to find radon because conventional methods of measuring radiation do not detect it in the air.

He added: 'We eliminated viral and bacterial infections but also obtained test results that ruled out the possibility of radiation sickness too.

'We also failed to find any evidence that toxic chemicals were buried in the area as many locals claimed.'

Initially, medics who examined the dozing villagers found they were suffering from excessive fluid in the brain but could not work out why.

Desperate measures: Local government officials in Kalachi (pictured) are now considering plans to move the village entirely

Infected: Children affected by the mystery illness are so dizzy they can barely stand up by themselves and spend days at a time in bed

Nightmare: Professor Leonid Rikhvanov from the Department of Geo-ecology and Geo-chemistry said the 'toxic gas' induces its victims 'into a dream like state'

Doctor Egor Korovin, who examined the victims, said: 'In medical terms they are suffering from encephalopathy, a disorder of the brain but the cause is unclear.

'Scans have shown that many of the sufferers have excessive accumulation of fluid in their brains.'

HOW TOXIC IS RADON? According to the National Cancer Institute, radon decays quickly, giving off tiny radioactive particles. When inhaled, these radioactive particles can damage the cells that line the lung. Long-term exposure to radon can lead to lung cancer, the only cancer proven to be associated with inhaling radon. There has been a suggestion of increased risk of leukemia associated with radon exposure in adults and children however, the evidence is not conclusive. Radon is present in nearly all air. Everyone breathes in radon every day, usually at very low levels. However, people who inhale high levels of radon are at an increased risk of developing lung cancer. Advertisement

Last summer, 60 people were taken to hospital suffering from the condition which leaves people feeling dizzy, unable to stand, fatigued and with memory problems.

Children affected by the mystery illness could barely stand up by themselves and spend days at a time in bed.

Scientists recently stepped up their investigation after locals complained the situation was getting worse.

It is thought nearly one in five of Kalachi's 600 residents have been affected by the strange sleep disorder.

Scientists stepped up the investigation recently after locals complained that incidences of the strange sleeping disorder were getting worse, with nearly one in five of the village's 600 residents now affected.

They said the fact that some miners remained unaffected because they have built up a natural immunity to radon.

Alsu Shjeladeva, a local resident, said some men from the area had gone down the shaft in one of the mines and detected a sweet smell while down there.

The 54-year-old told Russia Today: 'We are afraid of what lies in store. We're afraid that we may all fall asleep.'

Ghost town: Kalachi's neighbouring town Krasnogorsk has been deserted since the closure of the neighbouring uranium mine

Terrifying discovery: A Russia Today film crew found radiation levels at a filled in mine shaft were 16 times higher than normal background levels

Top secret: In the Soviet era, Krasnogorsk was a secret and 'closed' uranium mining town run directly from Moscow

Another resident Igor Samusenko, whose son suffers from the condition, said: 'He runs around and then he gets inert, starts staggering.

'When he turns his head his eyes stay fixed at what he was looking at. If you try to wake him it seems the wants to open his eyes but can't. Sleepy valley, sleepy hollow, that's what people call us.'

Lyubov Belkova, 60, claims to be the first resident to have fallen asleep in April 2010 and has since suffered seven separate episodes.

She was diagnosed with ischemic strokes but then her neighbour began displaying the same symptoms. Some have even reported suffering from vivid hallucinations.

In September 2014, a Russia Today film crew reported radiation doses 16 times higher than would be expected from background radiation near the entrance of the abandoned mine.