Empty nest syndrome is a feeling of grief and loneliness parents may feel when their children move out of the family home, such as to live on their own or to attend a college or university. It is not a clinical condition. Since young adults moving out from their families' house is generally a normal and healthy event, the symptoms of empty nest syndrome often go unrecognized. This can result in depression and a loss of purpose for parents, since the departure of their children from "the nest" leads to adjustments in parents' lives. Empty nest syndrome is especially common in full-time mothers. From Wikipedia
