Your comment identifies that my above comments aren't really depression -- more of a dissapointing lull, and should not be confused with a real clinical level of depression which I'm not sure I've ever experienced.
I can only speak from my own experience. Taking that into account from the points you identified that is not depression, rather a state of being knocked down and overwhelmed. Something that in my experience you can push through and learn from.
Depression is different. The best way I can explain it is if you've ever experienced the kind of euphoria associated with a deep connection with someone else. Not just lust but a deep connection or love - depression is the exact opposite of that and just as powerful.
Unlike being in love, you may not know if you're actually depressed or just experiencing what I have taken your points to be as a state of being knocked down.
