While some modern dictionaries offer "homesickness" as a meaning of nostalgia, this feels like a relic. In common use, they just don't mean the same thing: Homesickness is distressing, while nostalgia is kind of nice; homesickness is about place, while nostalgia is about time [sources: Werman, Hirsch].
It's not reminiscence, either. In reminiscence, we recollect. In nostalgia, we feel. Reminiscing may lead to nostalgia, though [source: Leardi].
What exactly is nostalgia, then, besides tough to nail down? It's the complex emotion we sometimes feel when we fondly recall old times — a "sentimental longing or wistful affection for the past" is how the Oxford Dictionary puts it. The nostalgic state is bittersweet, a mixture of the happiness of mentally reliving cherished times and the sadness of knowing they're gone forever — that how we felt in those times is gone forever.
I'll never again know the carefree, unadulterated joy I felt in camp.
Those cherished times are usually social ones, starring us. They probably involve family and friends, took place in childhood or young adulthood and are often at least personally significant, possibly momentous [source: Routledge]. People all over the world experience nostalgia recollecting graduations, weddings, family reunions, birthdays, holiday dinners and vacations with loved ones [sources: Routledge, Tierney]. If movie and TV writers are to be believed, first kisses, senior proms, college road trips and riding bikes with neighborhood kids until dusk are nostalgia fodder, too.
But here's the thing: Our recollections aren't quite accurate. We often unconsciously edit out any bad stuff. (I was actually pretty afraid I was going to swallow one of those minnows.) In this way, the past events and emotions we nostalgize about never really existed [source: Hirsch].
Nostalgia is a complex state, yet it's as common as it gets. Far from a disorder, it seems to be part of the human condition. Most people nostalgize at least once a week [source: Tierney]. Some people are particularly prone to nostalgize, including chronic worriers, who may experience it as an escape from present-day anxiety [source: Tierney]. Nostalgia also peaks in transitional age ranges, notably the teens through 20s (from dependence to independence) and over 50 (from "middle-aged" to "senior") [source: Leardi]. Where am I going? and Where have I been? are straight lines to nostalgia [source: Holak and Havlena].
Songs, smells, photographs and loneliness will trigger nostalgia, too, though some more powerfully than others.