Actually, it makes total sense, just a weird kind of sense.

It became your normal. Now that that normal is being shaken up, your mind isn't totally sure how to adjust. Maybe some of the lingering negativity too makes you feel like it's wrong for you to be happy (at least, that's what happens to me when I'm in a less-depressed state).

I don't know how to get past it, but I can tell you it's not that weird.