Sleep paralysis is a phenomenon in which an individual, either during falling asleep or awakening, they temporarily experience an inability to move, speak, or react.
It is a transitional state between wakefulness and sleep where the subject they are unable to move their muscles.
People who experience sleep paralysis often they experience terrifying hallucinations which they are unable to react to.
They hallucinations involving a person or supernatural creature terrifying them, accompanied by a feeling of pressure on their chest and difficulty breathing.
Other subjects they experience a hallucination type involving a home intruder accompanied by a feeling of dread.
One hypothesis sleep paralysis is a result of disrupted REM sleep, which normally induces complete muscle numbness to prevent sleepers from acting out their dreams.