One of the common problems reported today is poor sleep. A 2019 survey across 12 countries (including India) found that about 62% of the participants (n > 11,000) do not sleep very well, and only 10% reported sleeping extremely well . Many studies suggested that sleep problems could be seen among school-going youngsters of age 10–17 years as well as among the population over 50 years of age [2,3,4]. Sleep is one such autoregulatory mechanism of the body, essential to perform many vital physiological functions such as development, clearing of brain waste, and modulation of the body’s immune responses , and hence deprivation of this function increases the risk of disorders like stress, anxiety, depression, obesity, hypertension, dyslipidemia, diabetes, cardiovascular diseases, cancer  and can potentially lead to substance abuse and even suicidal ideation. At the same time, efficacious behavioral treatments such as mind–body therapies, biofeedback, guided imagery, hypnotherapy, mind–body movement, meditation, relaxation techniques, yoga, and even spiritual practices or other contemplative techniques, that help reduce stress and improve sleep exist alongside pharmacological management of insomnia and sleep disturbances [7,8,9,10,11,12,13,14,15].
Research establishes that such practices significantly improve sleep quality, duration and other aspects of sleep, both in clinical as well as non-clinical populations: meditation in particular impacts various components of the body’s sleep generating mechanisms and alters them . Although there are various kinds of meditation, there are commonalities between various techniques, and all of them are beneficial to some degree or other for the reduction of stress, anxiety, depression, and improvement of pain [10,11,12,13, 15, 16]. A recent meta-analysis by Rusch et al. , which focused on RCTs involving populations with significant sleep disturbance, also compellingly suggests that meditation improves sleep quality even in such populations . The beneficial impact of certain types of meditation on sleep has been extensively studied, particularly mindfulness meditation and mindfulness-based stress reduction (MBSR) exercises, along with Vipassana, other kinds of transcendental meditation (TM) and Sudarshan Kriya Yoga [11, 17,18,19]. An inverse association for higher frequency of practice of Sudarshan Kriya Yoga and lower odds of poor Sleep Quality (OR = 0.52; 95% CI 0.28–0.94) has also been revealed . However, so far as we know, no study discusses another type of meditation, known as the Hollow and Empty Meditation (HEM) and its effect on sleep.
Taught as part of Advanced Meditation Program (AMP), a meditation retreat offered by the Art of Living Foundation, the practice of HEM leads to a non-cognitive/non-affective state. HEM differs from normal meditation practices as it is only practiced in a retreat setting and not as a home practice. It is practiced only with a trainer guiding one through the process and not by oneself. It also presupposes a familiarity with the well-researched breathing technique of Sudarshan Kriya Yoga (SKY) [16, 21,22,23,24]. Ideally experienced once in 6 months, HEM has been practiced for more than 40 years, and its effects are said to last a long time. However, scientific evidence around its benefits is lacking. This study is one of the first research studies on it, and adds to the currently limited research around meditation retreats and their residual benefits, and expands its scope by studying the effect of HEM on sleep quality and duration. It also investigates whether HEM has residual effects post practice by assessing these impacts on day 40 as well.