Why do we feel nostalgia?

Nostalgia was once considered an illness confined to specific groups of people. Today, people all over the world report experiencing and enjoying nostalgia. But how does nostalgia work? And is it healthy? Clay Routledge details the way our understanding of nostalgia has changed since the term was first coined in the late 17th century. [Directed by Anton Bogaty, narrated by Addison Anderson].