<p>High-ventilation breathwork is a breathing practice that involves deep, accelerated breathing over an extended duration (&gt; 15&#xa0;min). Variants of this technique appear across diverse traditions, from Pranayama to Holotropic and Conscious-Connected breathwork (CCB), and have been reported to benefit physical and mental health, often by evoking non-ordinary states of consciousness. However, scientific research on the effects and mechanisms of high-ventilation breathwork is still in its infancy. This study examines the physiological and experiential effects of CCB. Specifically, we characterize subjective breathwork experiences using Natural Language Processing analyses of semi-structured phenomenological interviews, and relate them to changes in heart-rate variability. Finally, to disentangle the effects of the breathing technique itself from context effects, we tested whether accompanying the session with music altered its impact. Our findings show that CCB consistently triggers non-ordinary states of consciousness, intensifies emotional experience, and leads to reduced HRV during the session, but increased HRV post-session. Notably, this post-session increase in HRV was larger for subjects who experienced a wider range of emotions during the session, but not predicted by HRV fluctuations during the session. This suggests that post-session HRV improvements might be a product of emotional release (catharsis) rather than a purely physiological stress adaptation (hormesis, i.e., an adaptive improvement in function following time-limited, manageable physiological stress). Finally, none of these effects were significantly impacted by music, underscoring the central role of the breathing practice itself.</p>