Nightmare Disorder and Isolated Sleep Paralysis.

Nightmare disorder and recurrent isolated sleep paralysis are rapid eye movement (REM) parasomnias that cause significant distress to those who suffer from them. Nightmare disorder can cause insomnia due to fear of falling asleep through dread of nightmare occurrence. Hyperarousal and impaired fear extinction are involved in nightmare generation, as well as brain areas involved in emotion regulation. Nightmare disorder is particularly frequent in psychiatric disorders and posttraumatic stress disorder. Nonmedication treatment, in particular imagery rehearsal therapy, is especially effective. Isolated sleep paralysis is experienced at least once by up to 40% of the general population, whereas recurrence is less frequent. Isolated sleep paralysis can be accompanied by very intense and vivid hallucinations. Sleep paralysis represents a dissociated state, with persistence of REM atonia into wakefulness. Variations in circadian rhythm genes might be involved in their pathogenesis. Predisposing factors include sleep deprivation, irregular sleep-wake schedules, and jetlag. The most effective therapy consists of avoiding those factors.

Sleep paralysis in adolescents: the 'a dead body climbed on top of me' phenomenon in Mexico.

AIMS: The aim of the present study was to evaluate the prevalence and characteristics of sleep paralysis in adolescents using a folk expression. METHODS: Three hundred and twenty-two adolescents (mean age, 15.9 +/- 0.88 years; 66.8% female) from three high schools in Mexico City completed both a self-reported questionnaire, including a colloquial definition of sleep paralysis and the Epworth Sleepiness Scale. RESULTS: A high proportion of the adolescents (92.5%) had heard about the 'a dead body climbed on top of me' expression and 27.6% of them had experienced the phenomenon. Sleep paralysis was present in 25.5% while the prevalence rate for hypnagogic/hypnopompic hallucinations was 22%; 61% had experienced >or=2 episodes in their lifetime. The mean age of onset was 12.5 +/- 3 years. Sleepiness scores for the subjects who had experienced at least one event were not significantly different from subjects who had not experienced any. In 72% of cases, the episodes were composed of both sleep paralysis and hallucinations while 20.2% consisted of only sleep paralysis and 7.8% of only hallucinations. The number and characteristics of events were not significantly different between adolescents with only one episode and those with two or more episodes. CONCLUSIONS: The characteristics of the 'a dead body climbed on top of me' phenomenon suggest that is identical to sleep paralysis and a frequent experience among Mexican adolescents. During adolescence, sleep paralysis seems to be a recurrent phenomenon frequently accompanied by hallucinatory experiences.

Felt presence: paranoid delusion or hallucinatory social imagery?

Cheyne and Girard characterize felt presence (FP) during sleep paralysis attacks as a pre-hallucinatory expression of a threat-activated vigilance system. While their results may be consistent with this interpretation, they are nonetheless correlational and do not address a parsimonious alternative explanation. This alternative stipulates that FP is a purely spatial, hallucinatory form of a common cognitive phenomenon-social imagery-that is often, but not necessarily, linked with threat and fear and that may induce distress among susceptible individuals. The occurrence of both fearful and non-fearful FPs in a multiplicity of situations other than sleep paralysis attacks supports the notion that FPs are hallucinatory variants of social imagery and that they are not necessarily bound to threat-activated vigilance. Evidence linking FPs with anxiety disorders supports the notion that the distress they evoke may be mediated by a more general affective distress personality factor. To illustrate the predominantly spatial character of FP hallucinations, similarities between FP and phantom limbs are summarized and the possibility that these two phenomena are parallel expressions (self- vs. other-presence) of a mirror neuron system is considered.