Maybe I'm just weird, but I've had mood swings and rage along with my depression and anxiety for as long as I can remember. They're not what I would call usual symptoms of the problems, more like secondary symptoms. They seem to stem from being so frustrated about the depression or anxiety, not knowing how to cope, dealing with unsupportive behavior from loved ones, etc.
I definitely know the feeling. The other day I was so mad at my boyfriend because he used a rude tone with me, I threw my pen and stapler and was muttering to myself. Then I saw a feel-good post on Facebook and found myself grinning stupidly, only minutes later.

It could also be from medication, I found I had much more rage when I was on Prozac.