Nostalgia is about close others (family members, friends, partners), momentous events (birthdays, anniversaries, vacations), and settings (sunsets, lakes). It is a self-relevant emotion (as the self is invariably the central character in the narratives) but also a social emotion (as the self is almost always surrounded by close others). It is also bittersweet, albeit mostly positive. And it is triggered typically by aversive conditions, such as negative affect or loneliness.
Importantly, nostalgia, once evoked, re-establishes psychological equanimity. It elevates mood, self-esteem, and a sense of social connectedness; it fosters perceptions of continuity between past and present; it increases meaning in life; and it “fights off” death cognitions. Finally, nostalgia has motivational consequences, as it facilitates approach-oriented (e.g., prosocial) behaviour.