Imagine falling into a sound sleep, when suddenly you wake up and you can’t move a muscle. Sounds frightening! But it’s an experience that many people have at some point in their lives.
This weird phenomenon is known as sleep paralysis, where an individual cannot move, speak or react for a brief moment when falling asleep or awakening. It is a transitional state between wakefulness and sleep, which is often accompanied by hallucinations.
Hallucinations, such as the presence of someone in the room or someone sitting on your chest, are common and may make it difficult for the person to breathe. Physical experiences like a strong current running through the upper body are also common.
Sleep paralysis is relatively common, according to a 2011 systematic review published in Sleep Medicine Reviews. The review analyzed 35 studies reporting lifetime sleep paralysis rates of more than 36,000 participants in total.
Researchers found that 7.6 percent of the general population experiences sleep paralysis, rising to 28.3 percent in high-risk groups, such as students who have a disrupted sleep pattern. Among people suffering from mental disorders, such as anxiety and depression, 31.9 percent experienced episodes of sleep paralysis.
This study sheds light on the need for more research on sleep paralysis to determine its impact on an individual’s physical and emotional state. Also, its relation to psychiatric and other medical conditions should be further analyzed.
When Does Sleep Paralysis Occur?
Usually, sleep paralysis occurs within two specific times during the sleep cycle.
- While you are falling asleep, which is known as hypnagogic or predormital sleep paralysis. As you fall asleep, your body slowly relaxes and you may notice that you cannot move or speak.
- While you are waking up, which is known as hypnopompic or postdormital sleep paralysis. During sleep, your body alternates between REM (rapid eye movement) and NREM (non-rapid eye movement) sleep. At the end of NREM, your sleep shifts to REM, where the eyes move quickly but the rest of your body remains very relaxed. REM is the deepest part of your sleep cycle when your brain has vivid dreams. At this time, the muscles of your body are essentially turned off so that you do not act out your dream with your body. If you wake up before your REM cycle is over, you become fully conscious but your body is still in the REM sleep mode, leaving you unable to move voluntarily.
What Types of Hallucinations Occur in Sleep Paralysis?
Three types of hallucinations can occur during sleep paralysis, according to a 1999 study published in Consciousness and Cognition.
- Incubus: In this type, people feel intense pressure on their chests and feel they cannot breathe. Here, the body is still in REM breathing mode.
- Intruder: Here, people experience the feeling of a presence, fear, and visual and auditory hallucinations. It is described as a “hypervigilant state of the midbrain”, where people may be aware of even the smallest stimuli.
- Unusual bodily experiences: In this type, people have an out-of-body experience like flying or floating. Here, different areas of the brain are active at the time the person awakens.
Who Can Have Sleep Paralysis?
According to the American Academy of Sleep Medicine, people experience sleep paralysis for the first time between the ages of 14 and 17. It can affect men and women of any age group and it is estimated that it occurs in between 5 and 40 percent of people.