Yep...I think we can all relate to that feeling. I think that's one slight downside of this site, is that we're all kind of going through similar problems so it's hard for some of us to give useful advice when we're struggling ourselves. I will say that when you're in that type of mood...nothing is gonna make you feel better, except time. That's why I like taking long walks when I'm bitter and depressed. Often times I'll take a long walk, take a shower, eat something, and just do whatever I can to pass the time. That's all you can really do.
And I don't necessarly think this type of thing is so unhealthy, either. Maybe your emotions kind of blow up on you because you stuff them down a little too much? I've noticed that I literally feel better for days after I have a good cry. I don't cry too much, I kind of wish I could do it on command, cause god **** do you feel better after you've sobbed into your pillow for a few minutes. Being depressed, angry, etc. is well within the usual range of human emotions, and your brain has a very clever way of making sure you deal with everything. You just gotta let the negative emotions cycle through...at the end of the day those emotions are trying to tell you something. Stress and all other negative emotions are your mind's way of telling you that something is wrong.
Just try not to let the negativity swallow you. But hey, it's gonna once in a while. And that's OK. As long as you don't shoot up a post office or something.