A cognitive approach to understanding mood swings and bipolar disorders is provided, with the interpretation of changes in internal state as a central explanatory factor. The model explains how attempts at affect regulation are disturbed through the multiple and conflicting extreme personal meanings that are given to internal states. They prompt exaggerated efforts to enhance or exert control over internal states, which paradoxically provoke further internal state changes, thereby feeding into a vicious cycle that can maintain or exacerbate symptoms. Counterproductive attempts at control are classified as either ascent behaviours (increasing activation), or descent behaviours (decreasing activation). It is suggested that appraisals of extreme personal meaning are influenced by specific sets of beliefs about affect and its regulation, and about the self and relations with others, leading to an interaction that raises vulnerability to relapse. Pertinent literature is reviewed and found to be compatible with such a model. The clinical implications are discussed and compared to existing interventions.