Where the hell did THAT come from?

I've kind of been drifting along the last month or so, generally on a pretty even keel, even when I've been sorting through some things in my mind. Not in a bad mood, not in a great mood, but definitely in a significantly improved mood. The mornings are good, the workday is okay, evenings are nice and a chance to wind down with perhaps a glass of wine and relax before going to bed and repeating the cycle.

And then I hit a day like today when, all of a sudden, I'm so fucking irritable for no apparent reason. Seriously, just the fact that someone is breathing is enough to set me off today. And the woman who sat across from me on the bus this morning and kept moving her legs? I could have screamed!

And I'm argumentative, which isn't really me. I mean, sure, if you know me you know that I'll pick up on any slight inaccuracy or mistatement and I'll start belaboring that point, but this is different. This is me actually almost looking for arguments, picking arguments. And I'm one of the most non-confrontational people I know. (No, really, I am. Really. Fine, don't believe me, but I am.)

I have no idea where this comes from. I'm not PMSing, if that's what you think. Not the right time for that. Everything is going great, bills are paid (for a change), social plans have been made/are in the making (for a change), I've got pretty new clothes and books and things (for a change), I have my house back all to myself, I have trips to New York and London planned, I've started a self-improvement kick.

So I'm left asking myself, Where the hell did THAT come from? Does this happen to anyone else, or am I the only irrational neurotic freak like this?