Sleep paralysis and the science behind it
Imagine you wake up abruptly from your peaceful sleep. You try to move, but your body is not responding. Some sort of dark presence is sitting on your chest, keeping you from making the slightest move. You try to scream, but you can't do that either!
This is not a scary nightmare, but a very real phenomenon - its name is Awareness of Sleep Paralysis, or ASP. This scenario is extremely scary and different cultures from all over the world have attributed it to all sorts of evil supernatural presences, but it turns out it is nothing but a harmless glitch in the process of REM sleep. Studies show it is far more common than you would expect, with a large part of the population experiencing it at least once in their lifetime.
Sleep paralysis is a perfectly normal process that our bodies undergo during sleep - this is what keeps you from actually running around when a monster is chasing you in a nightmare, and why no kind of violent movement from a dream will ever affect your real physical self. This is supposed to happen every time we sleep and usually starts long before our dreams even begin, while its failure is usually the cause of sleepwalking. Most people don't even know sleep paralysis exists, since we are completely unconscious when it occurs, but from time to time someone will happen to become conscious: simply put, one's body wakes up before the mind. This is how Awareness of Sleep Paralysis happens, and there is nothing to be scared about when it does.
Only in the mid-twentieth century did we realize that sleep is not just a passive state or our existence - on the contrary, our brains are extremely active throughout it. We are now just beginning to understand how sleep, and also how the lack of it can affect our physical or mental health and our everyday functioning.
Our nervous system controls the entire process of sleep through neurotransmitters that act on different groups of brain cells. Serotonin and norepinephrine are the neurotransmitters that keep us awake, and they are produced by the neurons in the brainstem. When we fall asleep, neurons at the base of our brain begin to "switch them off" in order to induce it.
Sleep usually consists of five stages that progress in a cycle and then start over. From the light sleep of the first stage, where our eyes move very slowly and our muscle activity decreases, we enter the second stage – eye movement stops completely and brain waves slow down. The third and fourth stages are called deep sleep – the brain produces almost nothing but extremely slow "delta waves" and the person is extremely difficult to wake up. The final stage sets in 70 to 90 minutes after we fall asleep, and is called REM, standing for "rapid eye movement" - our breathing fastens, our eyes move frantically in various directions, our heart rate and blood pressure rise, but the muscles of our limbs become temporarily paralyzed. Moreover, in this stage the body loses the ability to regulate its own temperature, so extreme temperatures can disrupt the REM process.
When this stage is disrupted one night, the next dose of sleep we get will not follow the normal progression of the cycle, but switch directly into extended periods of REM, trying to catch up. There are many factors that can affect the sleep cycle - food, medicines, caffeine, nicotine or alcohol can all alter the neurotransmitters controlling the entire process. This is why, for example, REM can fail to set in in patients taking antidepressants or people who try to "cure" insomnia with a bit of alcohol.
The REM is best known for being the magical realm where dreams occur. But what is a dream after all? First of all, the dream can be defined as a form of thinking that occurs when there is a minimal level of brain activity, but the external stimuli and the "selfsystem" are both shut down. However, dream is also a realistic experience, but we can only analyze it in the form of what we remember in the morning. So basically, the dream is the recollection of a small fiction produced by our mind when our sense of self is "out of order".
Setting aside the endless array of possibilities opened by Sigmund Freud and psycholanalysis, science still does not really know why exactly do we dream. However, studies have shown that REM sleep stimulates certain regions of the brain that are responsible for learning, and especially learning mental skills. This may explain why REM takes up a larger part of sleep in infants than it does in adults. Other views state that dreams are nothing but the cortex's attempt at making sense of the chaotic, random signals it receives during REM.
There are also experimental studies that have proven that rats deprived of REM sleep only live for about 3 weeks, while their fully-rested peers typically have a life span of 5 weeks. Moreover, the deprived rats also had a weaker immune system and an abnormally low body temperature. Apparently, our nervous system cannot function properly without sleep. Deprivation leads to poor memory and concentration, sometimes even to hallucinations and mood swings if prolonged. Moreover, studies have shown that activity is reduced in parts of the brain that control decision-making, emotional processes and social interactions, so REM sleep helps us maintain a balance in everyday social and emotional functioning.
However, from time to time, someone happens to become conscious during sleep, and notice their paralysis. Consciousness brings the natural reflex of movement, and so they panic because they can't. To make matters worse, they are not entirely awake but not asleep anymore either, somehow caught in-between, and this fuels their struggle, leading to distress and agitation, all doubled up by hallucinatory states, since they are not out of the dream phase yet. This is why it is not uncommon for people to "see" demonic presences, monsters, witches or all sorts of other unfriendly creatures attacking them, as the reason behind their incapacity to make a move.
The terror experienced during ASP has inspired a wild range of mythical enemies all over the world. Many contemporaries have attributed this phenomenon to alien abductions, but our predecessors proved to have a much more vivid imagination. Incubi and succubi, the male or female demons that sneak up during sleep for an unwanted sexual encounter with a powerless human, may have been imagined as a supernatural explanation for ASP. Eugène Thivier's sculpture Le Cauchemar (The Nightmare) from 1894 and Henry Fuseli's painting with the same title from 1781 both depict this very scenario, with young women attacked by demons during their sleep.
The "old hag" spirit is another example of such mythical explanations. In Mexico, ASP is attributed to the spirit of a dead person and it is called "Subirse el Muerto", which literally translates to "dead person on you". In America, many people have reported demonic nighttime attacks during the Salem witch trials, but we now know there were much more logical explanations behind them. In Scandinavia, the presence is known as a Mare. In Turkey, ASP is blamed on a djin that can be chased away with certain prayers to Allah, while in Thailand, the cause is considered to be Phi Am, a ghost from popular culture, which is often used to cause suspense and horror in local comic books. In the famous novel Moby Dick, there is an episode where the protagonist Ishmael experiences ASP in the form of an evil presence appearing in his room.
Most of the times, ASP ends when the sufferer eventually wins over and regains the ability to move. This usually happens due to large quantities of adrenaline being released because of all the panic and anguish, forcing the body to wake up and catch up with the mind. However, it is not uncommon for the person to wake up and realize it was nothing but a dream.
Researchers from Penn State University in Pennsylvania state that less than 8 percent of the population experiences awareness of sleep paralysis, but it is widely believed that most sufferers are extremely reluctant about discussing their nightly terrors, for fear of being judged as "crazy", mentally unstable, hallucinatory etc. It has been noticed, however, that ASP tends to occur more often in students and psychiatric patients, and it seems like there may be a link between it and panic disorders. There are also plans for future studies investigating any links with post-traumatic stress disorder. However, the only conclusion here is that there is comfort for sufferers when they are willing to do their research: what used to be blamed on demons and monsters for centuries has a very logical explanation, and once you get to know it, you understand that there is nothing to be afraid of.