I have suffered from depression my entire life. It is organic...due to imbalances in my brain. Abuse may have caused those imbalances or triggered the gene that in turn causes depression (mental illness runs on both sides of my family). My depression is never so simple as to be anger turned on myself. It can be triggered by any number of factors, most often by a cluster of stressful and/or sorrowful events. The emotions that lead to it are most often grief, misplaced guilt, anxiety, long bouts of severe physcial pain (I have multiple autoimmune disorders), suffering of any kind by others, as well as myself, etc.
It is not triggered by anger and certainly not by anger I have failed to acknowledge. In my early therapy, I learned that failing to acknoweldge emotional or spiritual pain guaranteed an episode. My considerable anger at that time in my life was expressed...quite loudly on occasion. There were very good reasons for that anger and I held on to it because it felt so much more powerful than anguish, fear, or anxiety. As it denied the reality or truth of the experiences over which I was angry, it was very unhealthy, but not depressing. It took several years of therapy to resolve that anger. While I felt a sense of freedom and "lightness," I continued to be depressed.
This notion, taken as truth within our polpular culture, as well by many mental health service providers, is so harmful. It also easily leads to a kind of circular logic. If you refuse to admit you are angry and that anger is turned inward, you are in denial. it can lead to failure to find the real triggers for a patient's depression and lead to years of unsucsessful therapy. As Lisa points out below, it's usually a cluster of events that leads to depression. For myself, a survivor of childhood and adult abuse, those events touch the part of me which is most wounded. I am in an episode right now and have called what lead to it a "Perfect Storm" of stressors and emotion..