My thoughts are always positive ones

A well-tuned instrument still goes out in a cold room. Tuning isn't a permanent state, it is what you return to, and a piano nobody plays drifts flat just as reliably as one that gets used every day.

Minds work about the same way. Nobody holds a pitch continuously, and the people who seem to are usually just quicker at coming back — an hour of low weather instead of a fortnight of it.

So the thing to measure isn't whether a dark stretch turned up. It is the return time. That number moves, slowly, with sleep and daylight and one or two people who know how you actually are.