Loneliness is as strong a predictor of early death as alcoholism and smoking 15 cigarettes a day, and it turns out you don't actually have to be alone to feel lonely.
"No one talks to me other than myself, and my voice comes to me as the voice of a dying man. With you, beloved voice, with you, the last vaporous remembrance of all human happiness, let me tarry an hour longer. With your help I shall deceive myself about my loneliness; I shall lie my way back into society and love. For my heart refuses to believe that love is dead, cannot bear the terror of the loneliest loneliness. It compels me to talk as though I were two."Back to the WSJ
Evolutionary psychologists say the lonely feeling developed to alert humans—social animals who rely on each other to survive—that they were too close to the perimeter of the group and at risk of becoming prey.
Spending time alone is more fun when it is by choice. When it is the result of loss, separation or isolation, people are likely to experience it as loneliness. Homesickness, bullying, empty-nesting, bereavement and unrequited love are all variations on the theme. Loneliness isn't depression, which is a lasting feeling of deep sadness and hopelessness and should be treated by a professional.