The rapid expansion of Over-the-Top (OTT) streaming platforms has significantly altered global entertainment consumption, particularly among Generation Z, a demographic deeply embedded in digital ecosystems. Psychological thriller content—marked by suspense, emotional intensity, and morally ambiguous narratives—has emerged as one of the most engaging genres on these platforms. This study investigates the cognitive, emotional, and behavioural effects of psychological thriller OTT content on Gen Z, with a specific focus on its implications for social sustainability. Using a quantitative research design and survey responses from 227 participants, the study examines viewing patterns, emotional reactions, binge-watch tendencies, sleep disruptions, shifts in ethical perceptions, trust, social behaviour, and changes in real-world risk perception. Results reveal that psychological thrillers significantly influence behavioural psychology, with strong evidence of increased emotional arousal, heightened cognitive engagement, and altered social perceptions. Statistical analysis, including ANOVA on behavioural and frequency-based Likert scales, confirms significant variation across psychological and behavioural dimensions. While participants display high interest in complex narratives and suspense, the findings also indicate potential risks such as emotional fatigue, overthinking, anxiety, sleep disturbances, and reduced offline social interaction. The study highlights the need for balanced and sustainable media consumption and provides recommendations for OTT platforms, educators, mental-health professionals, and policymakers to promote healthy engagement and digital well-being among youth.