A 24-year-old woman with borderline personality disorder calls her DBT individual therapist during a crisis, reporting an overwhelming urge to overdose on her medications after a breakup. Her emotional arousal is extremely high and she is unable to engage in any cognitive processing. The therapist coaches her to fill a large bowl with ice water and submerge her face for 30 seconds while holding her breath. Within minutes, the patient reports a noticeable decrease in her emotional intensity. The therapist then coaches her through paced breathing and progressive muscle relaxation. A PMHNP reviewing this case asks which physiological mechanism accounts for the rapid reduction in arousal following the ice water intervention. Which of the following is correct?