Sleep Paralysis is an unsettling experience when a person feels as if they are physically paralysed and unable to perform any voluntary movements. It is usually experienced just as the person is falling asleep or waking up, and can be quite disturbing.
The cause of sleep paralysis is a protective physiological function that has evolved to prevent our body moving around when we are dreaming. Instead of physically acting out a dream, our brain blocks nerve signals to the large anti-gravity muscles in our limbs and torso. This creates the sensation of paralysis, and quite often a constricting feeling, like there is a person or a weight pressing down on our chest.
Due to the nature of this physiological function, sleep paralysis almost invariably occurs during REM episodes when we are dreaming, and so if we waken suddenly from a dream, we can feel paralysed with the dream imagery still lingering in our perception. This can lead to a variety of hallucinations. Sleep paralysis usually occurs when we are stressed and have been deprived of REM sleep, so when we fall asleep we go straight into a REM episode with our bodies being insufficiently relaxed.
