The word nostalgia is derived from two Greek words – nostos, meaning 'homecoming', and algos, meaning 'pain'. The medical professionals who coined the word nostalgia in the late 18th century were describing a serious emotional and physical condition, not the current meaning of wistful thoughts of earlier times. Originally, nostalgia was viewed as a crippling condition that rendered sufferers incapacitated by despair or intense homesickness. Soldiers suffering from nostalgia were often pulled off duty in order to recover their sense of purpose.

Indeed, nostalgia was considered a legitimate condition for voluntary release from military service even through the 1860s. If a soldier became too overwhelmed by thoughts of home or the life he left behind, his abilities as a fighter could be compromised. The damaging effects of nostalgia were a major problem for militaries and other government agencies around the world for hundreds of years. Only with improved treatments for melancholia and depression did the clinical definition of nostalgia begin to fade from history.

Almost everyone has experienced nostalgia in its modern sense, as a wistful memory of childhood or a strong feeling of homesickness. Nostalgia can also trigger a sense of euphoria as a pleasant memory is recalled. In fact, a number of industries and services depend on their customers' feelings of nostalgia and longing. Toy companies routinely bring back favorite childhood toys of an older demographic, while television production companies reissue older titles to tap into the viewers' sense of nostalgia. The popularity of collectibles stores also points to the commercial value of nostalgia.

While nostalgia in reasonable doses can provide a sense of comfort for stressed-out adults, too much nostalgia can have a negative effect. It is very common to believe that an earlier decade was preferable to present day conditions, but that viewpoint can be misleading. People who grew up in the 1950s may remember hula hoops, Elvis Presley and penny candies, but they usually don't indulge memories of McCarthyism, repressive roles for women and a lack of racial equality. Every decade has its positive and negative aspects, so an unrealistic sense of nostalgia may create an unhealthy distortion of reality. Some people can get caught up in feelings of nostalgia that make their current lives seem mundane or unfulfilling by comparison.

Painful feelings of nostalgia can often be addressed by acquiring a beloved item or planning a visit to a childhood hometown. Nostalgia may hurt more when combined with feelings of hopelessness or helplessness. The power of knowing you can revisit parts of your past can help to lessen the effects of homesickness or nostalgia. It is important to remember, however, that feelings of nostalgia are normal and healthy, but making a conscious effort to live in the past may not be. If a healthy sense of nostalgia seems to be turning into an unhealthy depression, you should seek professional counseling to regain a proper balance.