Why do we feel nostalgic?

For many years, those experiencing extreme nostalgia were diagnosed as depressed. Indulging in memories of the past was seen as a sign of homesickness and refusal to enjoy the present. It was seen as lack of commitment to the future and a burdening attachment to the past.According to John Tierney of The New York Times, living in the past, or nostalgia, was deemed a disorder since the 17th century when a Swiss physician attributed soldiers’ mental and physical ailments to their longing to return home.