"Free-floating anger". This term probably doesn't even exist, but it seems to be the best thing I can think of to describe my mood today.

For some reason I feel abnormally angry, and I have absolutely no idea why. There's nothing particularly annoying happened today. People seem to be generally happy and pleasantly-disposed towards me, and I'd say the sun were shining unless I lived in the UK, where we don't so much get sun as partially-glowing cloud cover. I can think of no reason, rational or irrational, for my bad mood, yet it's still there.
Even things I would usually find relaxing, such as mass alien slaughter and random bouts of humour haven't improved my mood much.

I had thought that perhaps I was tired, or maybe I had one of my more-frequently-occurring-than-I'd-like headaches, or something to explain this ill temperament, but I can't seem to find anything. I feel no more tired than I usually do and my head feels fairly fine (*touch wood*).

The odd thing is, that now I've written about it, I don't seem nearly as angry as I was 10 minutes ago. That's even more perplexing to me. Normally writing isn't something that I do all that often, and it normally doesn't tend to affect my mood even when I do write.
Guess I'll have to wait and see what happens for the rest of the evening. Hopefully I won't frustrate too many people should my negativity return.

Note: you have no idea how difficult it was to find different ways of saying "bad mood". Perhaps I should vary my writeups more in future...