I hate days when it feels like my mood/mental health might be getting ready to take a serious downward turn but it's too early to be sure. I always start quizzing myself about whether I've had enough sleep, whether I've remembered to eat good meals, whether I have PMS, whether I've had a medication change, or whether some obvious life event could be the cause.
This seems to annoy my therapist. He says I always "go for the physical first" when looking at how I'm feeling. I don't really care that much what he things.
I hope that you'll be able to sleep tonight, and that tomorrow will be better.