Traditionally, nostalgia has been conceptualized as a medical disease and a psychiatric disorder. Instead, we argue that nostalgia is a predominantly positive, self-relevant, and social emotion serving key psychological functions. Nostalgic narratives reflect more positive than negative affect, feature the self as the protagonist, and are embedded in a social context. Nostalgia is triggered by dysphoric states such as negative mood and loneliness. Finally, nostalgia generates positive affect, increases self-esteem, fosters social connectedness, and alleviates existential threat.
Sedikides, C., Wildschut, T., Arndt, J., & Routledge, C. (2008). Nostalgia: Past, present, and future. Current Directions in Psychological Science, 17(5), 304-307.