When I think about nostalgia I am reminded of the Milan Kundera quotation that reads: "The Greek word for "return" is nostos. Algos means "suffering." So nostalgia is the suffering caused by an unappeased yearning to return." I think that describes it very well. Here are the links to three articles on the topic that examine it a little deeper.
1) Nostalgia: On the Wistful Presence of Absence
This article says that the longing from nostalgia comes from "the indefinable sadness of life's finite essence slowly slipping away from us. Each look back subconsciously reminds us that there's that much less to look forward to—the sand in our hourglass trickling ever lower. Our lives that much more "used up." I suppose this is part of aging and something we will all experience more of as we become older. I do think that although nostalgia is natural we should never allow it to cause us to miss out on the life we are experiencing now. I believe that at any age there are new adventures to be had, new experiences to treasure, and new people to meet. In other words, this is a well written article, but don't let it depress you too much!
2) Nostalgia: Why we think things were better in the past
This article brings up a couple of really great points. First, it points out that nostalgia is so powerful that a large number of products have been created to appeal to our 'nostalgic tendencies.' Just looking around my room I know this is true, for I can see several items that I purchased primarily because they reminded me of something else! However, the article did reassure me that being vulnerable to such things does not mean I'm a weak person. It actually shares that "Research in 2008 showed nostalgia to be a feature common to the most resilient people" and "Sociable, emotional and motivated people are more likely to relish some reminiscence." A very interesting and surprising find indeed!
3) Nostalgia is Good Medicine
This article suggests that the reason we might be so prone to nostalgia is because it "promotes psychological well-being" and "fosters feelings of belongingness." Definitely worth a read!