Sleep Paralysis

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If you’ve ever woken up and been unable to move, you may have experienced sleep paralysis. Learn more about what causes these unnerving sleep hallucinations and how you can stop them.

What is sleep paralysis?

In the transition periods of waking up or falling asleep, individuals with sleep paralysis feel awake in the mind but paralyzed in the body. These hallucinatory episodes can be quite frightening and sleep hallucinations are thought to be the origin of stories of demonic or extraterrestrial visits. Studies performed in sleep labs show that while a patient with sleep paralysis is awake and aware of their surroundings, instruments measuring brain waves record their brain as asleep.

Imagine awaking to strange faces and voices but you cannot respond or wake up. Sufferers report an accompanying feeling of dread. Some feel they cannot breathe.

Some sleep researchers make the distinction between hypnagogic hallucinations (which take place in the transition from wakefulness to sleep) and hypnopompic hallucinations (in the transition from sleep to waking.)

Types of sleep paralysis

Individuals experiencing an episode of sleep paralysis often report one or more of these sensations:

  • Difficulty breathing, as if someone or something is crushing the chest
  • Inability to move the eyes
  • A feeling of dread or fear
  • Seeing or sensing an evil presence in the room

Throughout history people have recorded stories of visitors during sleep. A demon – called a succubus or incubus – is said to attack or molest the sleeper and through magic prevents the sleeper from fighting back. The first case histories of sleep hallucinations were published in 1664. Many report a witch is sitting on their chests, preventing them from moving. In some stories, the demon has sexual relations with the sleeper. In recent decades, the stories have often been of extraterrestrial visitors who use advanced technology or UFOs to stop the human from moving. One theory is that the mind constructs a story to try to make sense of the sleep paralysis.

There are three main categories of hallucinations that accompany sleep paralysis:

  • The intruder hallucination, where the individual senses another presence in the room, often wishing to do them harm. Researchers believe this is due to an overactive amygdala (the fear center in the brain). The subcortical thalamoamygdala pathway is a survival feature meant to alert the brain to danger, and it may become active during these hallucinations. Once the brain recognizes there is no danger present, it typically turns off. In sleep paralysis, it stays on longer than it should.
  • The incubus hallucination, where the individual experiences difficulty breathing, or chest pain or pressure. During parts of REM, airways may become blocked. If the individual begins to wake during this time when their muscles are immobilized and their breathing is shallow, they can interpret the breathing difficulties and muscle resistance as something pushing on their chest.
  • The out of body experience, where the individual feels like they are flying or floating, and sometimes sees themselves doing so. Unlike the other hallucinations, this one may be accompanied by a feeling of joy or elation. This hallucination can happen when the parietal lobe or angular gyrus is stimulated during sleep, and since the body isn’t moving, it confusing the brain about your body position.

What causes sleep hallucinations?

Sleep paralysis attacks typically happen in the first two hours of sleep, during or around the first REM stage of the night. The hallucination typically lasts from a few seconds to two minutes.

When we go into REM sleep our brain restricts our body from moving by blocking the signals to the body that tell us to move. This is so when you are running in your dream, you are not running in bed. The theory most widely accepted is that during an episode of sleep paralysis, the individual’s brain simply does not open up that block quickly enough after waking.

When a person is in the REM stage of sleep, his or her skeletal muscles are paralyzed. This condition is medically known as REM atonia. If the sleeper’s brain comes out of REM before the body, the person can become conscious while still having paralyzed muscles. Microarousals are common between sleep stages. The combination of a dream during REM and the odd sensation of being paralyzed while awake can cause subjects to report surrealist conditions. People report seeing ghosts or feeling someone sit on their chest.

Another hypothesis is that the brain does not truly awaken during these microarousals in which sleep paralysis is experienced, but only part of the brain is awake.  Other parts of the brain continue to dream, which the waking part of the brain sees as hallucinations.

The phenomenon could also be an artifact of the different sections of the brain falling asleep and waking up at slightly different times. Scientists using electrodes implanted in the human brain found the lower parts of the brain fall asleep before the higher parts. The brain falls asleep from the inside-out rather than from the outside-in. During this freewheeling period the brain is both asleep and awake and the narrative constructing cortex makes up its own reality.

How common are sleep hallucinations?

Estimates of the prevalence of sleep paralysis are all over the place; studies done in different countries produce vastly different numbers. One meta-analysis reviewed thirty five studies of sleep paralysis and found that 7.6 percent of the general population, 28 percent of students, and nearly 32 percent of psychiatric patients reported at least one episode of sleep paralysis in their lifetimes.

Sleep paralysis typically occurs first during the teenage years, and goes away with age, as demonstrated by more students experiencing it than the general population.

Doctors have identified certain factors that may aggravate the chances of sleep paralysis. These include:

Is sleep paralysis dangerous?

Almost everyone experiences sleep paralysis at least once or twice during their lifetime. Some people have it more often, and although it can seem creepy to the sleeper, it is not medically dangerous.

If the hallucinations are very scary or disrupt your sleep to the extent that you experience excessive daytime sleepiness, you should see a sleep doctor to rule out narcolepsy or another sleep disorder. They will ask you questions about your personal and family health history, your sleep patterns, drug use, and details about the hallucinations. They may have you undergo an overnight sleep study known as a polysomnogram that charts your brain waves while you sleep, or a Multiple Sleep Latency Test that tests how quickly you fall asleep to a nap during the day.

How to stop sleep paralysis and hallucinations

Sleep hallucinations often go away with age. However, many people continue to experience them throughout their lifetime, and wish to reduce or eliminate them. Even though sleep paralysis itself is harmless, it can cause problems by creating bedtime anxiety and making one fearful of falling asleep, which can exacerbate pre-existing depression, anxiety, or sleep disorders.

Lifestyle changes can offer relief for the mild to moderate sleep paralysis sufferers, such as:

For more extreme cases of sleep paralysis, patients are often advised to get used to the phenomenon. It does not require treatment unless the subject finds it unusually disturbing such that it bothers him or her. Treatment is usually psychological rather than medical, if any treatment is given at all.

For the more serious cases, medication in addition to lifestyle changes and behavioral therapy reduces the severity of the episodes and possibly reduces the number of episodes. Doctors may also prescribe antidepressants or the benzodiazepine Clonazepam – commonly used for patients with seizures – to help relieve sleep paralysis symptoms in severe cases.

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