An excerpt from the Wikipedia article on "nostalgia":
The term was newly coined in 1688 by Johannes Hofer (1669-1752), a Swiss medical student. The word is made up of two Greek roots (νόστος = nostos = returning home, and άλγος = algos = pain/longing), to refer to "the pain a sick person feels because he wishes to return to his native land, and fears never to see it again". This neologism was so successful that people forgot its origin. lost time and place, usually located in the near past. Homesickness is often given as a synonym for nostalgia.
During this period, from the late seventeenth century to the late nineteenth century, that doctors diagnosed and treated nostalgia, it also had other names in various languages — mal du pays (country sickness) in French, Heimweh (home-pain) in German, hiraeth in Welsh, and el mal de corazón (heart-pain) in Spanish.
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Sometimes the memories are brief flashes, as if straight out of a film. Sometimes they are more elongated and I dwell on them more thoughtfully. There is no real method to the order in which they appear to me. By this I mean to say that they seem to be from no particular era in my life. In fact, there are only a few things I can say about them for certain. I do know that they occur on a daily basis. I also know that I enjoy them a great deal. It is not as if I am displeased with my current affairs, by any means. I do not see my nostalgia as a form of escape from present day reality. It is only that there is a kind of incomparable satisfaction that springs forth from knowing that one of the few things we can know is this:
what is done is done.
Let it be noted that I have taken into account those people who would argue that there is nothing satisfying about such a concept. Those people would ask, "what about everything that is wrong with what has happened?"
I would respond by asking those people what they can do to make it right.
