Sleep paralysis is classified as a parasomnia associated with rapid-eye-movement periods (REMPs). The paralysis is consistent with atonia observed during normal REMPs produced by hyperpolarization of the spinal motoneurons originating in cholinoceptive neurons in dorsolateral regions of the pontine reticular formation. Estimates of RISP prevalence vary dramatically, yielding estimates between 6% and 40%. Sleep paralysis is often considered as a sleep-onset problem under the assumption that episodes occur at the beginning of the sleep period during Sleep Onset REM Period (SOREMP). Multiphase sleep-wake schedule (MPS) regimes likely produce high level of cognitive arousal precipitating episodes by increasing potential for waking during immediate post-interruption REMPs. Vestibular-motor (V-M) hallucinations likely arise via interactions between subcortical and cortical vestibular centers. RISP associated with a variety of affective disorders including depression, panic disorder, PTSD, and social anxiety. RISP has typically been thought to reflect anomalies of the functioning of monoaminergic and/or cholinergic neural systems.