The Effect of the Virtual Reality–Based Biofeedback Intervention DEEP on Stress, Emotional Tension, and Anger in Forensic Psychiatric Inpatients: Mixed Methods Single-Case Experimental Design - Lisa Klein Haneveld; Tessa Dekkers; Yvonne H A Bouman; Hanneke Scholten; Joanneke Weerdmeester; Saskia M Kelders; Hanneke Kip (JMIR Formative Research)