The quality and amount of sleep are indicative of secular shifts, including the increase in shift work, extended work hours, and constant availability of goods and services.1 Research conducted in Western populations has demonstrated that a decrease in the mean duration of sleep is associated with several health issues, including fatigue, excessive daytime sleepiness2 as well as alterations in metabolic and immunological functions3 and the endocrine system.4

In today's urban societies, an inadequate or excessive amount of sleep has been linked to negative health outcomes, such as hypertension5, morbidity1, obesity, type 2 diabetes6, poor self-rated health7, and respiratory disorders8 in both adults and children.9 Additionally, a variety of sleep disorders, including insomnia, have emerged as a worrying problem for people's health in China. According to a survey conducted on the general population at a national level, insomnia has a 21.4% prevalence rate, which includes having trouble maintaining sleep, having trouble starting sleep, and waking up too early in the morning.10 Several studies have indicated that sleep disruption is a significant risk factor for suicide- and stress-related health problems.11 Therefore, improvement in sleep quality is necessary to achieve optimal mental health, particularly for individuals who struggle with challenges linked to sleep.

There is a pressing need for developing more efficient and sophisticated scientific methodologies to enhance sleep quality. Limited research has been conducted on the impact of regular exercise on the subjective assessment of sleep quality among individuals.12 In a study conducted by Kezirian, Kamdar, Kaplan, and Dement (2004), it was shown that increasing the duration of sleep from around 7.5 hours to 8.5 hours had a positive impact on mood and enhanced vigilance levels in human participants.13 Additionally, a recent investigation conducted by Kezirian, Mah, Mah, and Dement (2011) explored the impact of enhanced sleep duration on the athletic performances of collegiate basketball players. In the present study, the sleep duration of the athletes, which typically ranged from six to nine hours, was extended by an additional two hours. This augmentation of sleep duration has several positive outcomes, including enhanced sprint times, reduced fatigue ratings, lower mean response times and drowsiness scores, heightened vigor, and improved shooting accuracy. Furthermore, both mental and physical well-being were enhanced during game practice.14 Nevertheless, an inquiry remains: Does forest sleep have a positive impact on human well-being? “Shinrin-yoku,” also known as forest bathing, is a prevalent nature-oriented practice that is widely observed in Japan. Recently, there has been an increased focus on utilizing it as a method for inducing relaxation and alleviating stress. The practice of “Shinrin-yoku” encompasses a range of health-related activities conducted within forest environments with the aim of improving both physiological and psychological well-being.15 Researchers are motivated to investigate the potential therapeutic effects of forest settings on individuals with depression and stress-related mental health disorders. Numerous nations, such as Japan and other European countries, have historically employed health resorts to ameliorate health issues, and forest environments are frequently linked to these establishments.16 The health of people has been shown to benefit from being in natural settings. Mitchell and Popham established a robust relationship between health status and the amount of greenery in residential areas in a population survey in the UK; the rates of death and heart disease were lower in regions near greenery.17 Kuo and Taylor (2004) suggested that green outdoor surroundings have a positive impact on attention-deficit/hyperactivity disorder symptoms in adults.18

Sleep can be measured using objective parameters. Nevertheless, the subjective impressions of individuals significantly influence the assessment of sleep quality.19 An alternative approach for assessing sleep quality involves the examination of brainwave patterns, namely those associated with delta, theta, and alpha waves, within the frequency range of one to nine Hz.20 The various stages of sleep are characterized by distinct frequencies. When an individual is awake and in a relaxed state with their eyes closed, alpha frequencies ranging from 8 to 13 Hz are observed. As one transitions into sleep stage 1, which is the initial phase of falling asleep, the theta frequencies ranging from four to seven Hz become prominent. In sleep stage 2, persistent theta frequencies accompanied by sleep spindles in the range of 11 to 16 Hz are observed. During sleep stage 3, which marks the transition into deep sleep, delta frequencies ranging from 0.5 to 2 Hz are present. Furthermore, in sleep stage 4, the delta frequencies are greater than 50 %. The sleep cycle, commonly known as a sequence, has a duration of approximately 90 minutes and is iterated until a state of awakening is reached.21

The use of brain stimulation throughout the sleep cycle, namely within the frequency range of one to nine Hz, has been observed to affect the overall quality of an individual's sleep in a manner that does not induce stress. This intervention is characterized by its non-intensive and non-invasive nature.22 Therefore, brainwaves are the most reliable source of sleep-related data. Previous studies employed the Profile of Mood States (POMS) to assess participant reactions15; However, the use of the State-Trait Anxiety Inventory (STAI) in sleep research has been infrequent. Furthermore, a limited number of psychological studies indicated that individuals have a compelling reaction to natural habitats, particularly forests, which are beneficial for mitigating stress and depression and promote psychological tranquility.23 However, the effect of forest habitat on physiological responses, namely those measured using electroencephalography (EEG), is unclear. The existing body of literature lacks scientifically rigorous and empirically grounded investigations of the therapeutic effects of forest sleep on cerebral functioning. Hence, the primary objective of this study was to elucidate the physiological and psychological ramifications experienced by adults engaging in sleeping activities in a forested environment.