Sleep paralysis

Sleep paralysis is a generally common condition, which involves a temporary paralysis of voluntary muscles before or after sleep, while other vital systems, such as the respiratory system remain fully functional. Furthermore, ocular movements can be made, but the person literally cannot move a muscle. There are two types of SP to be distinguished, hypnagogic and hypnopompic, the first one occurring when going to sleep, and the latter when starting to wake up. This condition is believed to be a continuous episode of REM sleep into a state of being awake. Because of the fact that during REM sleep dreaming takes place, in this stage there is a complete muscle atonia in order to prevent us from acting out the dreams. In this case also only ocular and vital systems remain intact, making it almost identical to the condition of sleep paralysis. However, the big difference is in the state of awareness, because while one is asleep during REM, he/she does not notice this paralysis, but it can become extremely frightening to experience it while awake.

Additionally in the majority of cases of sleep paralysis, different types of hallucinations can co-occur with the condition, which can be significantly increasing the terror experienced. In general three types of hallucinations are usually reported, intruder hallucinations (sensing somebody in the room), incubus hallucinations (sensation of being suffocated), or vestibular-motor hallucinations (illusionary movement, out-of-body sensation). 

The similarity of sleep paralysis to vivid dreams makes it harder to diagnose the condition using subjective measures. Self-reports by individuals might be biased, where one falsely thinks they are awake, experiencing sleep paralysis, while in fact they are still asleep, dreaming. To truthfully determine the presence of sleep paralysis, objective measurements should be used, such as using EEG, measuring brain activity that shifts from brain waves of REM sleep to brain waves that are observed when the individual is awake. 

Other conditions that sleep paralysis is linked to:

• Insomnia
• Narcolepsy
• Anxiety/depression
• High stress 
• PTSD
• Obstructive sleep apnea

References

Denis, D. (2018). Relationships between sleep paralysis and sleep quality: current insights. Nature and science of sleep, 10, 355-367. https://doi.org/10.2147/NSS.S158600