When I was in college, I had a bout of depression which I barely survived. It came on slowly and left even more slowly. Though the worst of it lasted only a few months, the entire awful experienced stretched over more than two years.
Since that time, I've been vigilent about not letting myself fall back into the dark abyss. Still, my struggles with depression come and go--albeit in a far less intense form than I experienced in college.
I do virtually everything which has ever been recommended to prevent or treat depression. I have lots of friends whom I meet regularly. I eat healthily, including plenty of fish and seafood. I exercise. I maintain my weight. I read the Bible, pray, and sing hymns. I don't abuse alcohol. I think positively. I express my negative feelings. I have enjoyable hobbies. I sleep enough.
In spite of all my efforts, I can't quite manage to totally banish depression from my life. It's like an old friend that keeps stopping by for a visit every so often. I've learned to endure, even ignore, the occasional visits, because I know they won't last long.
To make matters worse, I also suffer from recurrent bouts of anxiety. In some ways, the anxiety is far more difficult to bear than the depression. It is physically uncomfortable and distracting. I feel tightness in my chest. My heart beats faster, and my body feels generally "not right." The anxiety seems to originate in my chest and often refuses to leave for days, no matter what I try to do. Exercise is helpful, but (surprisingly) the most helpful thing is being busy doing some challenging activity. Going to work is quite helpful, even when I don't enjoy my job.
My mother also struggled with both depression and anxiety, as did her mother. My guess is that is it probably something genetic. I'm just grateful that I've learned to live with it. My grandmother and mother both struggled with alcoholism. I think it was their way to try to deal with the anxiety. Fortunately, I've taken a different path.