These are just a few questions I ask myself every time it happens to me. For those of you who have never experienced an episode of sleep paralysis, it is when you are aware of being awake, but cannot make conscious movements. It has occurred multiple times for me, usually upon awakening. I feel as if I am awake but trapped in my own body since I cannot move. I can open my eyes, but that usually makes it worse because it brings the idea of "being trapped" in my own body to life. Occasionally, I experience dream-like hallucinations as well. I get scared about it happening and I have hypothesized as to why it happens. My main hypothesis is that it occurs when I am dehydrated. Over the past few years, I have "self-treated" by chugging water after an episode. Recently, I have come to the conclusion that stress also must be a factor in my sleep paralysis as it has been occurring more frequently since being a grad student.
So what is sleep paralysis?
Sleep paralysis (SP) is characterized by short periods of time in which voluntary muscle movement is inhibited, but ocular and respiratory movements are active and ones sensorium remains clear (Sharpless and Barber 2011). It can happen upon falling asleep (hypnagogic or predormital sleep paralysis) or upon waking up (hypnopomic or postdormital sleep paralysis) (Johnson 2012). According to research, there are a few factors that predispose an individual to sleep paralysis (Golzari and Ghabili 2013). Factors include irregular sleep patterns, sleep deprivation, disturbances in sleep-wake rhythms, sleeping supine, alcohol consumption, and as I had hypothesized, mental stress. Sleep paralysis has been most commonly found in students and psychiatric patients (Sharpless and Barber 2011). Sleep disturbances have been found to be the link between these two populations (Sharpless and Barber 2011).
Sleep paralysis is considered an intrusion of rapid eye movement (REM) sleep. During REM, heart rate increases, blood pressure rises, eyes jerk rapidly, and skeletal muscles become temporarily paralyzed (NINDS 2007). REM sleep starts with signals from the pons that travel to the thalamus. The thalamus sends signals to the cerebral cortex. The pons also sends signals that are responsible for shutting off neurons in the spinal cord which is responsible for temporary paralysis of the limb muscles (NINDS 2007). The mechanism for which the temporary paralysis occurs is through GABA and glycine neurotransmitters that trigger REM paralysis by turning off motor neuron activity (Brooks and Peever 2012). Metabotropic GABAB and ionotropic GABAA/glycine receptors are targeted by these neurotransmitters and thus inhibit motor neurons (Brooks and Peever 2012).
Sleep paralysis occurs when wakefulness is partially reached but the body and part of the brain are still in REM. REM typically occurs after an hour or more of sleeping. If sleep paralysis is interrupting REM, how come I typically experience sleep paralysis upon waking up and others experience it when falling asleep? People who experience sleep paralysis upon falling asleep experience it due to another type of REM sleep called sleep-onset REM periods or SOREMPs (Santomauro and French 2009). But SOREMPs cannot explain sleep paralysis in people like me who emerge from an entire night of sleep and then experience the paralysis (Santomauro and French 2009). However, a similar mechanism has been proposed. Hypnopomic sleep paralysis is thought to be also caused by a mixing of both normal wakeful consciousness and REM consciousness thus leading to the feeling of being trapped, unable to move in your own body (Santomauro and French 2009).
Why does sleep paralysis occur?
From my research, there are several factors that seem to be correlated with episodes of sleep paralysis. Sleep paralysis, particuarly hypnagogic sleep paralysis, is a common symptom of narcolepsy (Santomauro and French 2009). However, you do not have to have narcolepsy to have sleep paralysis. Irregular sleep habits can causes irregularities in sleep-wake rhythms which are thought to lead to the disruption of REM sleep and thus sleep paralysis (Golzari and Ghabili 2013). Irregularities in sleep are often seen in students and psychiatric patients and thus these populations tend to see high rates of sleep paralysis (Sharpless and Barber 2011). Sleeping in a supine position has been correlated with sleep paralysis, but the mechanism is unknown (Cheyne et al 2002).
However, the only correlation I could find between sleep paralysis and dehydration was from a study done that found alcohol consumption has been found to trigger sleep paralysis (Golzari and Ghabili 2013). From this, I made the following connection: alcohol consumption leads to dehydration and thus maybe dehydration is the reason behind why alcohol consumption can lead to sleep paralysis.
My most recent hypothesis of sleep paralysis being correlated with stress does seem to be correct. Studies have found that panic disorders and post-traumatic stress disorders lead to a higher incidence rates of sleep paralysis (Santomauro and French 2009). In addition, anxiety which leads to sleep distributions also are correlated with higher rates of sleep paralysis. Depression has also been highly linked with sleep paralysis (Santomauro and French 2009).
Can sleep paralysis be prevented?
Since sleep paralysis is thought to be an interruption of REM sleep, life style changes that help to decreases sleep cycle disruptions can help prevent episodes of sleep paralysis. Maintaining a regular sleep pattern can help decrease sleep paralysis (Cheyne et al 2002). If the cause is stress related, anti-anxiety medications can help decrease episodes of sleep paralysis. If an underlying sleep disorders, such as narcolepsy, are the cause, diagnosis and treatment of that disorder is necessary (Cheyne et al 2002).
For now, maintaining a consistent sleep schedule and keeping stress levels low can be difficult as a graduate student. Therefore, finding ways to "break" the sleep paralysis is the best attack. From the research and from past experience, it seems that the best way to "break" the paralysis is to move a small muscle such as an oculomotor muscle or a finger or toe (Santomauro and French 2009). This has proven useful for me, but it takes repeated movements to "snap" myself out of paralysis. From the research, others have been able to get the attention of their bed-partner by making a sound. However, for some, like me, making a sound during sleep paralysis has been impossible (Santomauro and French 2009). After breaking the paralysis, it is important to get up and move around before trying to fall back asleep. If you don't, the reoccurrence of the paralysis is likely because you have not "risen" fully out of REM.
Sleep paralysis is not life threatening, it can just be very scary. I really dislike when it happens to me. From this research, I am going to try my best to keep my sleep schedule consistent as well as keeping stress levels at bay.
References:
Brain basics: understanding sleep, May 2007. National Institute of Neurological Disorders and Stroke. Available at: http://www.ninds.nih.gov/disorders/brain_basics/understanding_sleep.htm
Santomauro J, French CC. Terror in the night. Aug 2009. The Psychologist. 22(8): 672-675.
Cheyne, JA, Newby-Clark, IR, Rueffer, SD. Jan 2002. Relations among hypnagogic and hypnopompic experiences associated with sleep paralysis. Journal of Sleep Research, 8: 313–317. doi: 10.1046/j.1365-2869.1999.00165.x
Brook PL, Peever JH. July 2012. Identification of the transmitter and receptor mechanisms responsible for REM sleep paralysis. The Journal of Neuroscience. 32(29): 9785-9795.
Golzari SEJ, Ghabili K. March 2013. Alcohol-mediated sleep paralysis: the earliest known description. Sleep Medicine. 14(13): 298.
Sharpless BA, Barber JP. Oct 2011 Lifetime prevalence rates of sleep paralysis: a systematic review. Sleep Medicine Reviews. 15: 311-315.
Johnson K. Oct 2012. Sleep paralysis. WebMD Medical Reference. Available at: http://www.webmd.com/sleep-disorders/guide/sleep-paralysis?page=2
Christine,
ReplyDeleteI found this information about sleep paralysis very interesting! I too have experienced sleep paralysis, but only once. At the time I thought I had simply dreamt the whole thing because I couldn't imagine how I could have been awake and not been able to move. I remember lying supine which is unlike how I normally sleep (perhaps that was my trigger). As I began talking to some friends who have gone through the same thing, one said that she believed her episodes of sleep paralysis occurred when she felt guilty about something, which I suppose is related to the stress triggers.
You said that making small muscle movements helped break the paralysis for you. However, in my experience, no matter how hard I tried I could not move or speak. Since it was the middle of the night I simply went back to sleep and hoped someone would find me in the morning, but when I woke up I was fine. I'm curious, if you were able to wake someone up, how would they be able to help break your sleep paralysis? Would they just need to move a limb and the rest of the body is broken from the paralysis?
Additionally, do you think that sleep paralysis occurs throughout a person's sleep regularly and the majority of the time we just don't wake up to it? Or does it solely occur as a disruption of REM sleep?
-Kalina
Your post on SP is spot on! From what I've read before, I've learned that SP comes as a result of changes to sleep patterns that put the sleeper straight into REM sleep without needing to undergo the stages of non-REM sleep. As such, other triggers for paralysis come from shift work, jet lag, caffeine, or alcohol; from this, I can personally attest to jet lag and caffeine causing paralysis. Another cause for some of my paralysis episodes stem from sporadic naps taken during the daytime. Usually, I am accustomed to two hours during a nap, which perfectly alleviates me of sleep deprivation; however, I sometimes have to contend with only one hour given time constraints. It is during this one hour of napping that I usually experience SP. Perhaps it is because REM sleep occurs a little after one hour of sleep, and if you only nap for about an hour, it increases the likelihood that REM sleep would be disturbed, which would cause SP.
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