The prevailing view on positive emotions is that they correlate with and confer psychological health benefits for the individual, including improved social, physical and cognitive functioning. Yet an emerging wave of scientific work suggests that positive emotions are also related to a range of suboptimal psychological health outcomes, especially when the intensity, duration, or context do not optimize the individual's goals or meet current environmental demands. This paper provides an overview of the 'other side' of positive emotion, by describing and reviewing evidence supporting the emerging field of Positive Emotion Disturbance (PED). We review relevant emotion processes and key themes of PED and apply this framework to example emotional disorders, and discuss implications for psychological change and future research agendas.