What is Sleep Paralysis?
Usually we divide mental states into discrete categories. The two primary, binary mind states are Waking and Sleeping. But we know that waking is a continuum: tired, calm and alert, wired and ready to go, etc. And obviously even in sleep there are multiple stages, including REM-Sleep, which can be further split into active and phasic REM. But then, there are special mental states which are liminal. Liminal means having a foot in more than one realm at the same time. Cave paintings are filled with liminal creatures, part man and part beast. Liminal mind states include the likes of lucid dreaming (asleep with waking-like thought) and Sleep Paralysis.
Sleep paralysis occurs when the mind wakes up (more or less) from sleep, yet the skeletal muscle system is still paralyzed as when we are in REM-Sleep. This can be a very uncomfortable, even horrifying experience because we are not accustomed to having no control of our body when we are awake (unless you have a para- or quadriplegic condition). To add to this, the hallucinatory centers of the mind are not completely shut down while going through sleep paralysis, and so the threat-system of dreaming may superimpose visual and/or auditory hallucinations over what seems to be the real external environment. Is not uncommon during Sleep Paralysis to hear creepy noises, to see dark, grotesque beings, or to even feel physical sensations such as an invisible body pressing down on your chest. Scary is an understatement.
Anything that is likely to increase the odds of lucidity is also a possible trigger for Sleep Paralysis. In fact, some people who are prone to Sleep Paralysis learn how to use this liminal state to transfer into lucidity. If you can remember that the uncomfortable events are hallucinations, you can either slow down your breathing (you still have control of your diaphragm) and wake up, or you can remain still and gently imagine yourself entering into a lucid dream - until you do.