Scientists reveal the grisly truth about what happens if you DIE in a dream
On November 9, 1984 director Wes Craven unleashed a terror that would haunt the dreams - and nightmares - of horror fans for the next 40 years.
In 'A Nightmare on Elm Street', a generation of filmgoers were introduced to Freddy Krueger, a terrifying serial killer who hunted teenagers through their dreams.
Now, four decades after the classic film first clawed its way onto our screens, is there any truth to the idea that dying in a dream means you die in real life?
Speaking to MailOnline, experts say that, while you might not meet a bloody end while dozing, nightmares really could lead to serious health complications and even death.
During a nightmare, our bodies and brains are sent into a frenzy of activity as we live through whatever horrific scenario our mind has conjured up.
In some rare cases, that intense nocturnal fear could really kill you in your sleep by triggering a heart attack.
However, that doesn't mean you should start chugging coffee to stay awake like Elm Street's sleep-phobic teens.
In fact, scientists warn that the biggest danger associated with nightmares comes from missing out on valuable sleep.
As the horror classic A Nightmare on Elm Street turns 40 today, scientists reveal whether dying in a dream really could mean you die in real life
What is a nightmare?
Whether it involves having to take a test you didn't prepare for or being chased by a claw-handed murderer, almost everyone will have experienced a nightmare at some point in their life.
At a very simple level, a nightmare is just a particularly distressing dream in which we experience a high level of negative emotion such as fear, disgust, or disappointment.
Typically, people start getting nightmares when they are around three or four years old and start to experience them less often as they get older.
It isn't exactly clear what triggers nightmares at the physiological level, but Professor Tiina Paunio, a sleep expert from the University of Helsinki, told MailOnline that nightmares are likely related to parts of our brains associated with stress.
When we sleep, activity levels of noradrenaline, a brain chemical involved in our 'fight or flight' response, are usually low.
But during a nightmare, we see levels of noradrenaline spike in the amygdala and locus coeruleus - regions of the brain associated with fear, anxiety, and rage.
While the physiological origins of nightmares might be mysterious, their psychological causes are very well studied.
Nightmares typically occur during REM sleep late in the night when the areas of our brains associated with stress and panic start to activate
Professor Paunio says: 'Nightmares usually occur under emotional stress - so acute life stress is one risk factor.
'Lifestyle, in particular alcohol use, is another well-known risk factor for nightmares.'
Additionally, nightmares can be triggered by witnessing something frightening or traumatic.
That might explain why many Nightmare on Elm Street cast members reported experiencing nightmares after filming particularly scary scenes.
What happens if you die in a dream?
If you have ever had a nightmare involving your own death, then you know that the experience can be utterly terrifying and genuinely troubling.
Some experts suggest that this fear could be so powerful that it literally scares you to death.
When you get scared, your body jumps into its flight or fright response releasing a flood of chemicals including adrenaline and cortisol.
Experts say that you could really be killed by a dream of your own death if it is scary enough. During intense periods of fear our bodies release adrenaline which disrupts our normal heart rhythm in a way which could be fatal. Pictured: Heather Langenkamp in A Nightmare on Elm Street
While a jolt of adrenaline could be life-saving if you had to actually run away from a supernatural killer, this chemical is toxic to our organs in large doses.
When adrenaline comes in contact with the receptors on the heart's muscle cells it starts a chemical reaction which tells the heart to contract.
If a massive dose of adrenaline arrives, that signal won't turn off and the heart won't be able to relax, bumping the heart into a fatal abnormal rhythm.
Professor Paunio says: 'Generally, the health risks of nightmares are typically indirect and are linked to the causative factors that underly nightmares.
'In vulnerable individuals, for example, those with a heart disease, nightmares can indirectly contribute to death, although this is rare.'
That means dying in a dream could, in theory, mean you actually die in real life.
However, according to the American Heart Foundation, cases of being frightened to death are incredibly rare and typically involve some underlying heart conditions.
Likewise, the level of fear you would need to experience is likely to exceed even the most horrific of nightmares.
Suffering repeated nightmares causes disturbed sleep which can lead to increased risks of heart attack, diabetes, strokes, and suicide. Pictured: A scene from A Nightmare on Elm Street
Why dreaming might be dangerous
Even if you aren't likely to be killed in your sleep Freddy Kreuger-style, experts warn that frequent nightmares could be dangerous.
Professor Mark Blagrove, a psychologist and nightmare expert from Swansea University, says that there are two ways in which nightmares can lead to health problems.
'People could wake up from the nightmare and be fearful of going back to sleep,' Professor Blagrove explains.
'So one of the big problems with nightmares when they occur is that people can lose sleep as a result of it.'
For the average person, missing out on the odd night of sleep here or there isn't likely to be too much of a problem.
But for the two to six per cent of the population who suffer from frequent nightmares, those lost hours of sleep can start to pile up.
Professor Blagrove says: 'Pretty much everybody has nightmares but on average it's just a few a year.
While Freddy Kreuger can't really kill anyone in their sleep, some people have extremely high levels of 'dream distress' which means that repeated nightmares can lead to a spiral of stress and stress-induced nightmares. Picutred: Johnny Depp in A Nightmare on Elm Street
'But some people have them much more frequently, they may even have them every night.'
If your sleep is frequently disturbed it could lead to an increased risk of metabolic disorders like obesity and type two diabetes, heart attacks, and strokes.
Particularly worrying for those who might be experiencing nightmares as a result of PTSD, persistent sleep interruption also increases the risks of depression, anxiety, and suicide.
In addition to interrupting our sleep, the second way in which nightmares can be dangerous is by increasing our general stress.
Every person has some level of a trait called 'nightmare distress' which measures how badly we worry about nightmares.
Someone with extremely high nightmare distress might be scared of going to sleep for fear of having nightmares or even worry that their nightmares might be real upon waking.
Generally, our levels of nightmare distress decrease as we get older, but for some individuals, this can remain extremely high throughout their entire lives.
Professor Blagrove says: 'For some people who are having lots of nightmares, the nightmare itself can be another source of stress.
Studies have shown that having frequent nightmares means you may be at a much higher risk of suffering from long-term heart problems (stock image)
'You get a spiral where someone who's stressed has nightmares but then the nightmares become an additional form of stress for that person.'
Just like any other stress, that cycle of nightmares can start to cause serious health issues for those with high levels of nightmare distress.
What makes this so dangerous is that there is now a growing body of evidence which shows that frequent nightmares seriously increase your risk of having a heart attack.
Research published this year by Korea Univerity, Seol found that people who experienced nightmares were more than twice as likely to have risk factors for cardiac arrest.
Likewise, a study published last year by researchers from the Durham VA Health Care System, found that people with severe nightmares were more likely to display high blood pressure and heart problems.
This risk is so pronounced that research published by the European Society of Cardiology advised doctors to ask heart patients about their nightmares.
So, while being hunted in your dreams might not kill you then and there, frequent visits from Freddy Kreuger could still prove deadly in the end.
During the 1980s more than 100 men from the Hmong ethnic group living in America mysteriously died in their sleep, baffling medical experts. Some believed that the men were being killed by their nightmares
The real-life Nightmare on Elm Street
In 1981, the American Centre for Disease Control began to report on a mysterious serious string of deaths affecting young refugees from Laos and Cambodia.
Otherwise-healthy men from the Hmong ethnic group, usually aged between 25 to 44 years old, were dying in their sleep all around the country.
Despite none of the men having any history of heart conditions, autopsies suggested that their hearts simply stopped beating during the night.
A Nightmare on Elm Street Director Wes Craven says he was inspired to make the film after reading about a series of mysterious deaths which were attributed to a 'dream disease' killing people in their sleep (stock image)
Hmong elders claimed these deaths were the work of a spirit known as the Dab Tsog, an evil creature which attacks people by pressing down on their chests.
Some men were reportedly so scared by these deaths that they gave up sleeping altogether for fear of a visit from the Dab Tsog.
Overall, between 1981 and 1988, 117 cases were reported of what became known as Sudden Unexplained Nocturnal Death Syndrome, or SUNDS.
Reports suggested that fears of the mysterious dream deaths were keeping Hmog refugees awake. However, modern analysis suggests that Sudden Unexplained Nocturnal Death Syndrome is most likely to be caused by a genetic heart issue
As reports of SUNDS cases gained national attention, some researchers speculated that the fear induced by nightmares could be triggering fatal heart attacks.
Since the victims were largely refugees from the Vietnam War and the 'Secret War' in Laos, many assumed that their nightmares could be so intense that they were simply scared to death.
In interviews, Craven said it was reading about these attacks which formed the original inspiration for A Nightmare on Elm Street.
However, more recent research has cast some doubt over these more cinematic interpretations.
Modern genealogical approaches to SUNDS suggest that the condition is likely a congenital heart defect caused by a genetic condition.
This would explain why the deaths appeared to only affect men from one very specific ethnic group and not everybody experiencing PTSD.
Researchers have found that the genes associated with SUNDS could lead to ventricular fibrillation and acute cardiopulmonary failure as the heart rate naturally slows during sleep.
This means that SUNDS is not only extremely rare but is also unlikely to have any connection to nightmares.
