Greene, I can relate to that - "cloud of unknowing" might fit well. As a matter of fact, I find in my own experience that if I can put my finger on the root cause of a dark mood (it's very rarely the most recent or obvious reason), I'm half way out of the mood already. But it's not always simple to pinpoint the "why".

One thing I've learned to do is to reassure my hubby that my darker moods, while perhaps triggered by something he's said or done, very rarely actually have anything to do with him. If I'm brutally honest, I can usually trace the tendrils of that mood a long way down to a wounding that happened a long time ago.
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When you don't like a thing, change it.
If you can't change it, change the way you think about it.

(Maya Angelou)