Impulse purchases during flash sales may deliver instant satisfaction but can lead to financial burdens, guilt, and overall cognitive dissonance for consumers, especially in developing countries where knowledge of proper spending behavior is just beginning to be recognized. Prior research has prominently targeted the negative outcomes of impulse buying (IB), focusing less on its positive effects on consumers and retailers. The purpose of this research is to examine the effects of impulse purchases on consumer well-being (CW) in the South Asian context and analyze the mediating effects of the feel-good factor and return-exchange process as potential means of achieving a win-win strategy for consumers and retailers. Grounded in post-purchase behavior theory—integrating cognitive dissonance theory, regret theory, and the bottom-up spillover theory of subjective well-being—this study applies partial least squares structural equation modeling to cross-sectional survey data collected from 569 online consumers in Pakistan. IB exerts a positive direct effect on CW, with the feel-good factor emerging as the dominant mediating pathway and return-exchange behavior providing a secondary corrective route. The study resolves a longstanding paradox in IB research by demonstrating that flash-sale IB can enhance rather than undermine CW when post-purchase mechanisms are accounted for. It advances post-purchase behavior theory with novel evidence from South Asia and offers actionable guidance for marketers seeking to balance promotional effectiveness with consumer welfare.