Cultural Construction of Hypnagogic and Hypnopompic Hallucinations during Sleep ParalysisTo begin with, research suggests that sleep paralysis (SP) is usually caused by stress, irregular life and sleep pattern, sleep deprivation and abuse of alcohol and drugs. A significant amount of research also suggests a significant correlation between SP and PTSD, bipolar and anxiety disorders and some discuss that it also comes as a side effect of anxiolytic agents – drugs used to treat anxiety (Sharpless et al., 2015, p. 105). Some even suggest that it might signal the onset of a mental disorder. However, there is very little data to prove this theory and it is worth stressing that it does not necessarily have to occur in subjects experiencing mental disorders, the likelihood of healthy subjects experiencing SP is similarly present (Cheyne et al., 1999).  Approximately 25 to 40 per cent of general population report some SP experience (Solomonova, 2017), among those experiencing sleep paralysis, about 75 per cent will hallucinate in at least one bodily modality and about 5 per cent reports an episode of SP involving the full range of Hypnagogic and Hypnopompic Hallucinations (Cheyne et al., 1999). It occurs most often in adolescent population between the ages of 13 and 19 (Ohayon et al., 1999). Sleep paralysis can also vary in the frequency of occurrence. From being not present, to mild (occurring less than once a month), moderate (occurring once a month) to severe (occurring more than once a week) (Ohayon et al., 1999). Its duration varies from one to several minutes. Sensation of sleep paralysis is very often accompanied by anomalous sensory experiences, hallucinations that make this experience truly terrifying. Most literature define two types of such hallucinations: hypnagogic and hypnopompic experiences. Hypnagogic occur during the transition period from wakefulness to sleep or hypnopompic – from sleep to wakefulness (Mahowald et al., 2005).  People usually envisage ‘intruders, demons, spirits, evil ‘presence’ close by, unusual auditory, olfactory, physical sensations. It might include a sound of door opening or closing, bedsprings cracking, scratching, sometimes whispering sensations’ (Cheyne et al., 1999; p. 315). Often, these sensations occurring during sleep paralysis are depicted and believed to be causation of supernatural nocturnal assaults and paranormal experiences: ‘HHEs occurring during SP have been very often attributed to diverse worldwide cultural accounts of ‘nocturnal incubus/succubus assaults, spirit possessions, old hag attacks, ghostly visitations’ (Sharpless et al., 2015; p.20). These cultural accounts usually describe demons, spirits or a hag sitting on the victim’s chest and suffocating him: ‘I knew someone else was in the room. I could hear them moving around Then I know I felt someone sit down on the bed right next to me! I tried to scream… But I couldn’t’.’I have suffered from sleep paralysis and it was the scariest thing in my life. The first time it happened I thought it was a dream but I know I was awake’.’I cannot talk myself down from the terror and panic I feel’ – (Ohayon et al., 1999, p. 1196)This Night-mare imagery is often formulated by our language and folk myths and stories. ‘Mare’ comes from the same root as the German mahr and Old Norse mara, as supernatural being – usually female – who lay on people’s chests at night, suffocating them. ‘Some of the better-known historical references, in Western culture, to spirits of this sort are Greek—pan-ephi- altes (pan who leaps upon), graia, and mora (monster, ogre, spirit, etc.); Roman— incubus (one who presses or crushes) and lamia; German—mar/mare, hexendru ?cken (witch pressing), and Alpdruck (elf pressure); Czech—muera; Polish—zmora; Rus- sian—kikimora; French—cauchemar; Old English—maere and hagge; Old Norse—mara; Old Irish—mar/more; and Spanish—pesadilla (‘weight’) (Cheyne et al., 1999, p.325). There are of course, some cultural variations present in the meaning and depiction of night-mare, however, the fundamental experience seems to be consistent throughout time and across different cultures. This is very often explained in terms of experiential-source hypothesis that tries to explain why unconnected paranormal events are so similar in experiences (Sharpless et al., 2015). It holds that cultural myths and stories shape people’s views about the world, thus, also resulting in people have similar beliefs leading to experiences about supernatural occurrences. It also suggests that certain features of supernatural events are not bound to culture and are universal (Sharpless et al., 2015). Numerous studies have proven that across samples the similarity of experience is remarkable, thus leading to believe that not only neurological aspects influence the experience of SP, however, cultural narratives also have a say. ‘Only the specifics of interpretation (such as the nature and the cultural details of the entity) can vary substantially, and although culture is not the source of the experience, cultural beliefs do play an important role in determining the degree of salience of the night-mare’ (Liddon, 1967, p. 90).  Neurological construction of Hypnagogic and Hypnopompic Hallucinations during Sleep ParalysisUnfortunately, the cultural construction of such unusual sensations, does not satisfy the academic craving of understanding what actually happens in people’s brain when sleep paralysis occurs. Thus, this paragraph will contrast the previous presented cultural formation of HHEs with the proof of REM neurophysiology to explain the phenomenon. First factor will be labeled Intruder, which is the previously mentioned sensed demonic presence, consisting of feeling that someone is in the room next to you, auditory and visual hallucinations (Ohayon et al., 1999). Researchers discuss it is originating from ‘a hypervigilant state initiated in the midbrain in which ‘detection thresholds are lowered and biased toward cues for threat or danger’ (Cheyne et al., 1999; p. 321). ‘The fear involved in the sensations of sleep paralysis suggests that amygdala might be the central feature involved in the experience, and neuroimaging studies have also highlighted the importance of limbic structures or REM dreams’ (Cheyne et al., 1999; p. 322). It is discussed in the studies that the experience of a frightening presence and emergency reactions to dangerous or threatening events are generated via the subcortical thalamoamygdala pathways that direct more attention to the any imagined ‘demonic’ presence and leads to a person experiencing fear and other dream-like attributes in the reality. Another factor, is comprising pressure on the chest, breathing difficulties, which are attributed to ‘characteristics of REM respiration, including shallow rapid breathing, hypoxia, hypercapnia, and occlusion of airways’ (Cheyne et al., 1999; p. 330). ‘Increased airflow resistance because of hypotonia of the upper airway muscles and constriction of the airways can result in feelings of choking and suffocation leading to panic and efforts to overcome the paralysis and sensation of being choked’ (Cheyne et al., 1999; p. 330). A third factor, is labeled unusual bodily sensations, consisting of out of body sensation, floating experiences occurring in relation to body position, orientation and paralyzed ability to move (Cheyne et al., 1999). A considerable amount of research on sleep, suggested that REM dream imagery, together with the hallucinations induced by Sleep Paralysis involve amygdala complex and prefrontal cortical structures, which are similar with the pathways involved in hallucinations experienced by schizophrenic patients and hypnotically created hallucinations (Ohayon et al., 1999; Cheyne et al. 1999; Sharpless et al., 2015). Moreover, 70 per cent of sample that has experienced SP have reported experiencing enormous fear, and some argue, that in turn, that fear motivates additional experiences during sleep paralysis. Some type of sensed demonic presence may dramatically increase the alertness and vigilance to any endogenous (‘perhaps involving REM-related, oculomotor, middle ear, and primary sensory cortical activation’ (Koike et al., 2011; p. 327)) and exogenous environmental events.  Conclusion To conclude, sleep paralysis is a common, although often a very frightening experience. How one interprets SP depends on the available cultural constructions, myths and narratives and their credibility to the person pursuing to explain this remarkable experience (Hufford, 2005). With the advancement of neuroimaging techniques this phenomenon can now be explained using more scientific methods and drawing proof from subject’s brain activity. Research on SP has nonetheless a significant amount of limitations that make it difficult to study and draw precise conclusions about the problem. Most of the qualitative analysis of extensive sleep paralysis experiences result from self-report studies that are quite subjective and not necessarily accurate representations of it. Moreover, all studies on SP are retrospective in nature, and could influence the accuracy of one’s recovered memories after the occurrence. Furthermore, subjects in a large number of studies reported a fear of sharing their experiences with professionals or family members because of fear of negative reactions from others based on the supernatural content of the experience. Thus, this already indicates reporting bias making it even harder to research the sensation. Distressing experience of unusual sensations combined with hallucinations is sufficiently rare that subjects may fear to speak up about their experiences in public. Thus, this all adds up to underreporting and illusion of SP being an infrequent phenomenon. Finally, the lack of research results in some victims being reluctant to seek for help and as some studies suggested, possibly leading a person being afraid to go to sleep, developing insomnia, maybe sometimes even leading to interrupted everyday mental functioning and sometimes, mental illness. However, important to mention, sleep paralysis may also follow mental illnesses such as bipolar, anxiety disorder or PTSD.