Good days are good, bad days are bad, and there's nothing you can do about that. I find that if a bad mood stupefies you as to its origin, then, it's probably not your fault. You don't always need a reason. You can have two identical days with the exact same starting points, variables, circumstances and factors, and have the best day you've had in a long time in one, and be completely miserable the other, and have absolutely no guesses as to why. If it were deducible, which I do not think it is, it would be in the realm of chaos theory and not calculus, which even then would be difficult enough. Better to say, "my chemicals are off today." It's not me. It can't be me. I did nothing that could have possibly brought this on myself.
Not that this solves anything. I mean, I blamed it on my chemicals today and still felt like shit. But, if ever I had the impulse to start finding reasons as to the root of the cause, my shitiness intensified. God forbid I start asking myself, "what do I need to start changing about myself?" That's when the real stress kicks in. When you blame it on the chemicals, instead of blaming it on yourself, it at least leaves opportunity for a hard reset tomorrow. Usually, my chemicals do reset the next day. And I'll have no idea why I felt so bad yesterday. But, if I blame it on myself, then it almost always transfers over to the next day. Chemicals solve themselves over night. But self-condescending analysis of some deeply-rooted theoretical problems you may have carry over like an unsolved bug. And since they're only theories, you may never make progress, and trap yourself in a never ending cycle of self-pity.
Good days are good. Bad days are bad. It's as simple as that.