Sleep paralysis is a phenomenon in which a person either during falling asleep (hypnagogia) or awakening (hypnopompia), temporarily experiences an inability to move, speak, or react.

It is a transitional state between wakefulness and sleep, characterized by muscle atonia (muscle weakness). It is often accompanied by unusually powerful and terrifying hallucinations to which one is unable to react due to paralysis, and physical experiences (such as strong current running through the upper body). These hallucinations often involve a person or supernatural creature suffocating or terrifying the individual, accompanied by a feeling of pressure on one's chest and difficulty breathing. Another common hallucination type involves intruders (human or supernatural) entering one's room or lurking outside one's window, accompanied by a feeling of dread.