Sleep paralysis and the structure of waking-nightmare hallucinations

Sleep paralysis (SP) entails a period of paralysis upon waking or falling asleep and is often accompanied by terrifying hallucinations. These hallucinations constitute a waking nightmare (w-nightmare) REM experience and are the original referents of the term "nightmare." W-nightmare hallucinations are described by a three-factor structure involving experiences consistent with 1) threatening intruders, 2) physical assaults, and 3) vestibular-motor (V-M) bodily sensations. The present study assesses the reliability of this structure and some of the underlying measurement assumptions using several large samples of w-nightmare experients. Causal modeling further elucidated the potential causal relations among the three types of hallucinations. The first two factors appear to be strongly thematically and sequentially linked by an underlying theme of threat and assault. The third factor is relatively autonomous but appears to be sometimes recruited into the threat and assault themes. A theoretical model is proposed that combines REM mechanisms, a threat activated vigilance system (TAVS), and a bodily-self neuromatrix (BSN), as generators and organizers Of w-nightmare hallucinatory experiences. More generally, it is argued that these mechanisms underwrite two fundamental domains of conscious experience: the experience of an agent-inhabited world and that of a spatial-kinetic bodily self.