A head teacher has warned parents about the dangers of a new 'fainting' craze that's sweeping the playground.
The Choking or Passing Out Game involves children cutting off the oxygen supply to the brain until they pass out.
There are a number of ways they do this: one involves a child putting their thumb in their mouth and blowing hard, non-stop, until they pass out; another involves hyperventilating - breathing out in a succession of short breaths, depriving their brain of oxygen; in another practice, a child will lean heavily on a classmate's chest to prevent them breathing in; and in the most extreme case, children grab a fellow pupil by the neck, stopping the flow of oxygenated blood from the catorid artery to the brain.
This deprivation of oxygen to the brain is said to produce a sense of euphoria - but it is, obviously, highly dangerous.
The craze started in the States but has now reached school yards in Britain, prompting the head of a leading private girls' school to write to parents voicing her concerns about the so-called games.
In an email seen by Parentdish, the head wrote: "I am writing to you as it has come to my attention that there is a current trend among young people for choking or fainting 'games'.
"Apparently this has been played at parties and also in schools in the area. It is particularly popular among Year 9 students, but younger children sometimes copy older ones.
"I am very worried about this, as what appears to young people to be a harmless 'fun' activity can in fact lead to coma and possibly death.
"We will speak to the girls at school and we would be most grateful if you could reiterate this message at home.
"These games are extremely dangerous. Whilst girls involved in this will be in breach of the school rules, much more serious is the possible risk to life."
In the US, paediatrician Dr. Michael McKenna warned the craze 'could have a long-term impact' on kids.
He said: "Any time you're messing with oxygen supply to the brain you are putting yourself at extreme risk.
"Whether that's risk of death or whether that's risk of damage to the brain."
The warnings come a year after schoolboy Sam Thomas, 12, went into a coma after taking part in the craze.
Sam, from Newquay, Cornwall, blacked out while trying the stunt. He managed to get back to his feet and staggered to school but soon experienced pins and needles and started to feel faint.
He then passed out, hit his head on a tree on the way down which knocked himself unconscious.
Sam's parents Celia and Robert Thomas were called to the school, where they found their son's body 'shutting down'.
Sam was rushed to hospital where doctors feared he would suffer brain.
He was in the coma for 36 hours and has since recovered - but his family warned against children trying the prank.
Mum Celia said: "We had never heard of this thumb-blowing craze before, that's also what was really worrying. We were in disbelief that this could be so dangerous.
"It's caused death before and many more children have suffered brain damage. Children at that age don't understand things like this, there's no fear or danger.
"It's really important children understand the risks and we'd encourage parents to talk to their children about this."