A significant number of children are impacted by sleep disorders, reported in 25–62% of such children [1,2]. Among sleep disorders, parasomnia is more common in children than in adults. Parasomnia is one of seven major categories of sleep disorders registered in the International Classification of Sleep Disorder (ICSD) [3]. Parasomnia is a phenomenon in which abnormal movements, behavior, emotional experiences occur that are not desired during sleep or arousal. In ICSD-3, depending on the stage of sleep in which symptoms occur, parasomnias were classified into three clusters: non-rapid eye movement (NREM)-related parasomnias, REM-related parasomnias, and other parasomnias. The sleeping environment conditions often influence the occurrence and severity of parasomnia by sleep disruption. Any conditions that impair sleep maintenance and promote NREM fragmentation could increase the risk of parasomnias [4].

Co-sleeping, which is a natural part of parenting in Eastern cultures, would be one of the risk factors for sleep disruption in children. In the past, co-sleeping was an important means of survival to protect their children from danger such as predators, poisonous bugs, or even other humans during the night. As civilization developed, humans built houses and segregated family members into separate rooms. This change was accompanied by changes in the attitude towards co-sleeping. It has become a matter of choice for parents. With this change, several intense controversy over the hazards and benefits of bed-sharing emerged. The most typical topic is the case of sudden infant death syndrome, and the American Academy of Pediatrics issued guidelines warning against bed-sharing [5]. In Eastern cultures, co-sleeping remains highly prevalent. Several interesting factors such as positive maternal attitudes towards co-sleeping, number of children, and poor child health were associated with an increased incidence of co-sleeping [6,7]. Recent studies have reported that co-sleeping has adverse effects on infants’ sleep and increases arousal [7,8].

The influence of the bedroom environment is also critical. Sleep disruption can be triggered by poor sleep hygiene, including bright light, excessive noise, extreme temperature, mattress, and so on [9]. Last, the mothers’ dysfunctional belief in their children’s sleep can negatively impact the child’s sleep problems. For example, “If you don’t sleep well, you won’t be tall” or “If you talk nonsense while asleep, you have a mental problem” are typical concerns of parents. The parent’s dysfunctional belief could make a child’s sleep problem more severe and may terrorize the mother as well as the child. Of course, there is a relationship between sleep with growth hormone and sleep problems in children with developmental delay, but it cannot be reversed.

We hypothesized that factors related to the sleeping environment may affect the occurrence or progression of parasomnia. The purpose of this study was to identify the clinical features related to the sleep environment of childhood-onset NREM-related parasomnia and to develop a nonpharmacological treatment.

This study design was a retrospective review of the medical records of pediatric patients younger than age 18 diagnosed with parasomnia. Forty-two children with parents, who had visited the Pediatric Sleep Clinic at Asan Medical Center July 1, 2018–June 30, 2019, were included in this study. Cases with neurological damage, neurological diseases, or sleep difficulties attributable to other major mental illnesses such as psychosis and neurosis, were excluded from this study. The following information was reviewed through retrospective review of medical records: demographic information, the sleep pattern (bedtime, sleep onset time, wake-up time, naps), symptoms of parasomnias, the environmental sleep conditions (noise, brightness, room temperature, humidity, activities before bedtime), co-sleep environment condition (the number of people sharing a room at bedtime, patient’s night sweats, if the co-sleeping mother experiences coldness while sleeping) and mothers’ dysfunctional beliefs about the relationship between sleep and growth. Based on the above data, we reviewed the clinical features of parasomnias. SPSS version 21.0 software (IBM Corp., Armonk, NY, USA) was used for the statistical analysis. Statistical significance was defined by a p value < 0.05. This study was approved by the Institutional Review Board of Asan Medical Center (IRB No. 2019-0954), which waived the requirement for informed consent.

The mean age of subjects was 6.3 ± 3.1, and 27 (64.3%) children were males (Table 1). In sibling orders, the first child was the most common with 24 children (57.1%) followed by 11 second-born (26.2%) and one third-born (2.4%). The diagnosis was night terror (n = 21, 50.0%), sleepwalking (n = 8), confusional arousal (n = 2), and unspecified (n = 11). The average time of sleep pattern was as follow; bedtime 21:39 ± 0:54 pm, sleep onset time 22:13 ± 0:54 pm, wake-up time 7:37 ± 0:42 am and NREM-related parasomnia event time 1:09 ± 2:04 am (Table 2). The average number of family members and persons in a room while sleeping (co-sleep) was 4.1 and 2.8, respectively. Twelve of 33 (36.4%) children reported night sweats, while 16 of 33 (48.5%) mothers experienced coldness while sleeping together. Among the parents of the subjects, 22 (64.7%) parents believed that sleep disorders would adversely impact their child’s physical or psychological development. There was no significant difference in clinical characteristics between night terror and sleepwalking group except age (night terror 4.6 ± 2.8, sleepwalking 8.5 ± 2.1).

In the investigation of the relationship between NREM parasomnia and sleep environment, the number of co-sleeping members was relatively large, approximately three people in the same space. Interestingly, many mothers experienced coldness next to their sleeping children who were perspiring. More than half of the mothers had dysfunctional beliefs about sleep regarding their children.

The significance of the sleep environment in sleep problems is well known. Sleeping in a place that is noisy or too bright leads to sleep problems in the child [2,10]. The physical environment as well as the environment created by the co-sleeping mother can impact the child’s sleep. According to a previous path analysis study conducted by our team, sleeping problems occur more often in preschool children co-sleeping with parents than in children sleeping alone [10]. Co-sleeping with parents resulted in the mother perceiving her child as difficult to care for, and this mother’s stress was likely to be related to the child’s sleeping problems and sleep environment. Through the research results, we became interested in the relationship between co-sleeping and NREM-parasomnias. The term ‘cosleeping’ is a more comprehensive concept that includes ‘bed-sharing’ and ‘room-sharing.’ In this study, we did not distinguish bed-sharing from room-sharing.

We hypothesize one of the important reasons for the high prevalence of co-sleeping is that Korean bedrooms have a floor-heating system. The traditional floor-heating system heats the floor and promotes the circulation of warm air to warm the entire room. Sleep space-sharing is comparatively much easier because much more extensive space, the whole floor instead of just the bed, could be used for sleeping. From the perspective of space use and positive parental attitudes toward co-sleeping, a large number of parents opt to sleep with their children until they attend elementary school. Apart from the discussion on the safety of bed-sharing, a few studies have reported that bed-sharing may have other adverse impacts on the quality of infants’ sleep [7,8]. One of the most replicated findings was that co-sleepers showed more frequent awakening than solitary-sleepers [11]. Other studies using the polysomnography of mother-infants have reported that bed-sharing promoted infant arousal as well as an arousal of the mother [11-13].

In this study, we observed that children diagnosed with parasomnia perspired at night, but the mothers experienced coldness. This difference in subjective thermal perceptions between children and mothers may have made the mother act to warm the thermal environment. The exposure of heat or cold is one of the critical factors that can affect sleep stages [14]. Too much heat exposure by thermoregulatory behavior such as bedding or clothing can increase wakefulness and decrease slow wave sleep and REM sleep, but cold exposure did not impact the sleep stage [15]. We can assume that the mother who experienced coldness was not significantly impacted, but the child’s sleep with heat could be disturbed. Although the mother’s behavior was not investigated in this study, it is a topic worth examining in subsequent studies.

Sleep problems of children are related to their parents’ stress levels [16]. In this study, mothers who came to the hospital because of the child’s sleep problems were under much stress. They expressed concerns that ‘My child would have trouble growing if he or she couldn’t sleep well’ or ‘If my child talks nonsense while in asleep, it means that he or she may have a mental problem.’ Dysfunctional beliefs in sleep refer to maladaptive ideas and worry about sleep that are detrimental and increase sleep problems. It is one of the critical factors that impact actual sleep problems [17]. Chronic insomnia patients have more dysfunctional beliefs about sleep and complain more negativity about the consequences of insomnia compared to healthy sleepers [18]. These findings have been replicated in specific pediatric populations whose parents have dysfunctional beliefs about children’s sleep. The parent’s ideas about a child’s sleep problem may impact the child’s dysfunctional belief and their child’s actual sleep [19,20].

This study had limitations. First, it was a retrospective study. The data used in the analysis were insufficient to understand the clinical features regarding parasomnias fully. Second, the sample size was small, and there were no controls. Last, clinical characteristics were collected without sleep polysomnography. However, we observed the difference in subjective thermal perception between parasomnia children and mothers. The connection between the thermal environment and NREM sleep stage may have an implication of parasomnia. It remains unknown if co-sleep conditions may be related to the predisposition of parasomnia. Further understanding of the relationship between sleep environment and parasomnia could contribute to a better evaluation of the sleep environment and establish proper sleep hygiene education and treatment.