As someone who has experienced depression - fortunately mine was situational, and short lived - I can say that it is about the worst feeling in the world. I had been under extreme stress for a number of months, and then came home from work one night, sat on the couch, and couldn't interact with anyone. It was like being in a dark cloud, with no possibility of light breaking through - complete hopelessness. My wife called my father, who took one look at me and knew immediately what was wrong. He got me to talk about my stress, and once identified, he pitched in to help shoulder a workload that was crushing me. Without his help, I can't say what might have happened. It is still a constant reminder to never let myself get into that position ever again.