I don't know the exact definition, or how one distinguishes a shutdown from a period of situational depression.
I may have been situationally depressed, or in a shutdown, a few times before, sometimes lasting weeks or months.
One I recall, was after I quit my day job to go into freelance programming. After two months of trying to enter the field, I was very melancholic. I refused to go out, ate little, displayed little or no emotion, and generally stagnated for a bit before getting another day job. I call it going into hermit mode.
I'm not sure about either, though, because I find it impossible to stay that way continuously. I recall many times when I would be immersed in something interesting, excitedly working on something, and then tell myself "hey, I'm supposed to be in a funk."
I have to remind myself that I'm supposed to be depressed or apathetic. This realization, in a "shutdown/situational depression" usually makes me retreat further. Outside of one, I find it amusing. "This too shall pass," and all that.