Disasters disrupt societal functioning and precipitate a wide spectrum of individual and collective psychological responses. This chapter discusses the interplay between disaster events and mass behavior, with a focus on the South Asian context. It explores epidemiological trends, climate-linked vulnerabilities, and region-specific disaster response systems, highlighting the increased risk of psychiatric morbidity following such events. Common outcomes include post-traumatic stress disorder, depression, and anxiety, as well as mass behaviors like panic buying (PB), altruism, and community-led responses. A three-tiered model of mental health interventions is proposed, emphasizing trauma-informed, community-based strategies. The integration of mental health into disaster preparedness frameworks remains limited in the region, calling for sustained capacity building and policy reforms. It is hoped that this chapter will offer meaningful insights to guide policy, practice, and preparedness in addressing mental health outcomes and mass behavior during future disasters.