I often think it's like a split-personality thing. A mood or an irritation comes out of no where. I too have written or spoken something I regret (almost as soon as I have done it). Most of the time I kind of feel deflated, and irritation isn't the norm for me (I am gentle person), but I do get so annoyed that I clench my teeth sometimes and feel like hitting the wall or something.

I've heard mercury causes bi-polar, wonder if mild effects of that are mood-swings. Aggression can be caused by mercury, aswell as paranoia i.e. a sense of everyone is out to get you, conspiracy theories everywhere, no one likes you, outcast, and so forth.