Adverse Effects of Meditation: Autonomic Nervous System Activation and Individual Nauseous Responses During Samadhi Meditation in the Czech Republic Author: Silvie Kotherová1, Jakub Cigán2, Lenka Štěpánková3,4, Mária Vyskočilová5,6, Simona Littnerová7, Anastasia Ejova8,9, Milan Sepši10,11 Affiliation: <sup>1</sup> Department of Sociology, Andragogy and Cultural Anthropology, Palacký University Olomouc, Olomouc, Czech Republic. <sup>2</sup> Laboratory for the Experimental Research of Religion (LEVYNA), Department for the Study of Religions, Faculty of Arts, Masaryk University, Brno, Czech Republic. <sup>3</sup> Department of Psychology, Faculty of Social Studies, Masaryk University, Brno, Czech Republic. <sup>4</sup> Psychology Research Institute-Research departments, Faculty of Social Studies, Masaryk University, Brno, Czech Republic. <sup>5</sup> Department of Internal Medicine and Cardiology, University Hospital Brno, Brno, Czech Republic. <sup>6</sup> Department of Internal Medicine and Cardiology, Faculty of Medicine, Masaryk University Brno, Brno, Czech Republic. <sup>7</sup> Institute of Biostatistics and Analyses, Faculty of Medicine, Masaryk University, Brno, Czech Republic. <sup>8</sup> School of Psychology, Faculty of Health and Medical Sciences, The University of Adelaide, Adelaide, Australia. <sup>9</sup> School of Psychological Sciences, Faculty of Medicine, Health and Human Sciences, Macquarie University, Sydney, Australia. <sup>10</sup> Department of Internal Medicine and Cardiology, University Hospital Brno, Brno, Czech Republic. sepsi.milan@fnbrno.cz. <sup>11</sup> Department of Internal Medicine and Cardiology, Faculty of Medicine, Masaryk University Brno, Brno, Czech Republic. sepsi.milan@fnbrno.cz. Conference/Journal: J Relig Health Date published: 2024 Apr 12 Other: Special Notes: doi: 10.1007/s10943-024-02024-5. , Word Count: 204 Buddhist meditation practices, including Samadhi meditation, which forms the basis for mindfulness practice, are broadly promoted as pathways to wellbeing, but evidence of their adverse effects is emerging. In a single-group observational study with assessments of autonomic system before, during, and after Samadhi meditation, we explore the relationship between post-meditation nausea symptoms and the degree of change in autonomic system activity during meditation as compared to before and after in 57 university students (42 women; mean age = 22.6) without any previous experience in meditation or yoga practices. We hypothesize that nauseous feelings in meditation are connected to a rapid increase of activity in the sympathetic nervous system, as indicated by decreased heart-rate variability (HRV). We additionally explore links between meditation-induced nausea and two markers of parasympathetic activity: increased HRV and vasovagal syncope. Engaging in meditation and increased nausea during meditation were both associated with increased markers of HRV parasympathetic activity, but 12 individuals with markedly higher nausea demonstrated increased HRV markers of sympathetic activity during meditation. Vasovagal syncope was observed but found to be unrelated to nausea levels. Drivers of adverse effects of meditation in some individuals require further investigation. Keywords: Autonomic nervous system; Heart rate variability; Meditation; Nausea; Samadhi; Vasovagal syncope. PMID: 38605255 DOI: 10.1007/s10943-024-02024-5