Sleep paralysis (SP) is an inability to perform voluntary muscle movements at either sleep onset or upon awakening. It is considered a dissociated sleep state in which rapid eye movement (REM) sleep elements occur within a clear sensorium (American Academy of Sleep Medicine, 2014). Although common in individuals with narcolepsy, it can also occur in an idiopathic or 'isolated' form (i.e. ISP). SP has been associated with trauma, life stress, and numerous other variables (Denis, French, & Gregory, 2018).Fear and distress are frequently described emotional accompaniments to episodes of SP as well (Sharpless & Grom, 2016). The fear/ distress are not only due to the paralysis, but also to the accompanying hallucinations, which are usually negatively valenced (Sharpless & Kliková, 2019).Although much has been learned in the past two decades, relatively little attention has been paid to positive and/or pleasant aspects of SP. One study found that only 16% of episodes were pleasant (Lišková, Janečková, Kráčmarová, Mladá, & Bušková, 2016) and, in another, 17% of participants reported feelings of bliss (Cheyne, 2002). It is currently unclear why some individuals report more pleasant experiences than others. Is it possible that personality traits, levels of overall life satisfaction, or trauma history may predispose individuals to interpret and experience SP in more negative ways?There has also been some discussion of associations between SP and lucid dreaming. Both are REM sleep-based phenomena, with the latter being the ability to not only be aware of one's dreams, but also to directly effect changes within them (Denis et al., 2018). Reports from lucid dreamers indicate that SP can serve as a gateway to this practice (Denis & Poerio, 2017).

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Study Objectives Recurrent isolated sleep paralysis (RISP) is a rapid eye movement (REM) parasomnia characterized by a dissociative state with characteristics of REM sleep and wakefulness. Pathophysiology has not yet been clarified and very little research has been performed using objective polysomnographic measures with inconsistent results. The main aim of our study was to find whether higher REM sleep fragmentation is consistent with the theory of state dissociation or whether signs of dissociation can be detected by spectral analysis. Methods Nineteen participants in the RISP group and 19 age- and gender-matched participants in the control group underwent two consecutive full-night video-polysomnography recordings with 19-channel electroencephalography. Apart from sleep macrostructure, other REM sleep characteristics such as REM arousal index, percentage of wakefulness and stage shifts within REM sleep period were analyzed, as well as power spectral analysis during REM sleep. Results No difference was found in the macrostructural parameters of REM sleep (percentage of REM sleep and REM latency). Similarly, no significant difference was detected in REM sleep fragmentation (assessed by REM sleep arousal index, percentage of wakefulness and stage shifts within REM sleep). Power spectral analysis showed higher bifrontal beta activity in the RISP group during REM sleep. Conclusions The results showed an underlying persistent trait of higher cortical activity that may predispose patients with SP to be more likely to experience recurrent episodes, without any apparent macrostructural features including higher REM sleep fragmentation.

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Objectives. Psychometric properties of the Czech version of the Pittsburgh Sleep Quality Index (PSQI-CZ) have been evaluated only in patients with chronic insomnia, and thus, it is unclear whether PSQI-CZ is suitable for use in other clinical and nonclinical populations. This study was aimed at examining the validity and reliability of the PSQI-CZ and at assessing whether the unidimensional or multidimensional scoring of the instrument would be recommended. Methods. A total of 524 adult subjects from the Czech population participated in the study. The internal consistency of PSQI was evaluated using Cronbach’s alpha. The known-group validity was tested using the Kruskal-Wallis H test to verify the difference between patients with sleep disorders and healthy control sample. For testing the structural validity, a cross-validation approach was used with both exploratory factor analysis (EFA) and confirmatory factor analysis (CFA). For EFA, the maximum likelihood method with direct oblimin rotation and parallel analysis was used. Results. The internal consistency of PSQI-CZ items was moderate ( α = 0.75 ). Receiver operating characteristic (ROC) curve analysis showed high specificity (0.79) and moderate sensitivity (0.64) using an optimal cut-off score of 10. The EFA revealed a 3-factor structure with factors labelled as “sleep duration and efficiency,” “sleep disturbances and quality,” and “sleep latency.” The CFA showed that the emerged 3-factor model had a partly acceptable fit, which was better than other previously supported models. Conclusions. A high cut-off score of 10 is recommended to define poor sleep quality. Given the inconsistency of structural analyses, alternative scoring was not recommended. However, the individual components in addition to a total score should be interpreted when assessing sleep quality. We recommend editing and verifying the PSQI-CZ translation.

Mental activity in sleep often involves visual and auditory content. Chemosensory (olfactory and gustatory) experiences are less common and underexplored. The aim of the study was to identify olfaction-related factors that may affect the occurrence of chemosensory dream content. Specifically, we investigated the effects of all-night exposure to an ambient odour, participants’ appraisal of their current olfactory environment, their general propensity to notice odours and act on them (i.e., odour awareness), and their olfactory acuity. Sixty pre-screened healthy young adults underwent olfactory assessment, completed a measure of odour awareness, and spent three nights in weekly intervals in a sleep laboratory. The purpose of the first visit was to adapt to the experimental setting. On the second visit, half of them were exposed to the smell of vanillin or thioglycolic acid and the other half to an odourless control condition. On the third visit, they received control or stimulation in a balanced order. On each visit, data were collected twice: once from the first rapid eye movement (REM) stage that occurred after 3 a.m., and then shortly before getting up, usually from a non-REM stage. Participants were asked to report the presence of sensory dream content and to assess their current olfactory environment. Neither exposure, nor participants’ assessments of the ambient odour, or olfactory acuity affected reports of chemosensory dream content but they were more frequent in individuals with greater odour awareness. This finding may have implications for treatment when such experiences become unwanted or bothersome.