Whilst those factors may understandably cause occasional anxiety and depression in normal people, I think the depression being discussed here is a disorder perhaps termed chronic clinical depression, the result of a psychiatric disorder rather than caused by external influences?
Yes and No, Tailwheel.
Clinical Depression is not fully understood. I personally know a few people who suffer clinical depression that is generally thought to presented as a result of long-term, suppressed PTSD.
Teresa, the true and real effects of clinical depression are not diminished by the fact that there are 'hangers on' and malingerers. This occurs with every type of injury and illness. An acquaintance of mine committed suicide due depression about a month ago. Prima facie he had everything, and no reason to kill himself. More than 500 people turned up for his funeral.
Others I know have suffered flashbacks (it scares the sh!t out of you when you see this happen to someone) and PTSD symptoms years after traumatic events and they've attempted to suppress it. Years later they end up feeling very isolated and alone in their own head, because they can't talk about it with anyone who hasn't experienced the same thing. Without help this leads to depression.
I remember reading a few years ago that depression was actually one of the top three reasons for pilots losing their medical. Was it in FSM? With all the pressures and diminishing reward in this industry, Im not surprised.