Sometimes the reason you are feeling depressed has nothing to do with how things are going. My depression was caused by things that had happened in the past and that I didn't spend any time consciously thinking about. Dealing with that stuff took some work, but once I did, my depression lifted and hasn't returned.
Depression means, even if things are going well, you can't feel good about it.
Every effect is caused by something that happened in the past. The physical trauma of past situations reared its head. Sounds like an external factor to me.
Depression means, even if things are going well, you can't feel good about it.