I can attest that for me a regular sleep schedule works, but only so far.

At first it works kinda well as I feel increasingly settled as days go by, but at some point it seems being too restful kicks my mind into overdrive mode. From experience I can now detect such events, as it starts with a general feeling of everything being awesome, incredible energy, and fantastic happiness as I just am there (as with mindfulness and meditation), do many things† for a day or two, then everything inevitably crashes down†† as I start feeling increasingly but subtly anxious about minute details, followed by an increasing inability to focus and then comes listlessness. If a (even remotely) bad event happens right after the peak happiness state it can send me spiralling down even faster.

The only thing that can curb that is:

- an occasional short night (like getting 3 to 4 hours of sleep) once a week or so, after which I feel surprisingly refreshed. Sometimes it happens naturally as I wake up in the middle of the night and can't sleep, or go to bed late. But it better not last two or three days in a row or then the crashing down thing happens and it's even harder to climb up as the added sleep deficit combined with listlessness makes me very sleepy during the day. Note: I am largely unable to voluntarily control my sleep schedule.

- regular strenuous physical exercise, like daily, and for hours, and preferably outside. It seems I need to shoot my body through a satiated state of physical sensations in order to saturate my nervous system and keep my mind in check. I can skip a day or two but exercising, say, every other day doesn't check out as though the slope, while less steep, is still trending downwards. Outdoors is incredibly important to me as there are so much more physical stimuli (light, wind, sounds) and with greater variations than indoors.

- food and water. Regular hydration is capital for me, and some kind of mineral water is best. Tap water is out of question for some reason (strangely seems to upset my bowel/urinary system after a few days). A balanced diet can do wonders but it seems I can be derailed easily on that front.

I sort of picture my mood swings as f(t+phi) = mood, with f basically resembling a sine wave, and physical exertion seems to help me in adjusting phi. My general strategy to combat that is to try to hit that sweet spot where I'm right before the super-happiness point and attempt to ride the wave using exercise, caffeine and nicotine†† (sadly, using tobacco).

Honestly though I try not to put too much thought into it as I managed to turn anxiety about the situation into more like curiosity. Anyway on a larger scale the general mood trend is sensibly upwards as looked at retrospectively I'm climbing inch by inch out of that hole.

† I tried not being so hyperactive, pacing myself and not doing so many things but it doesn't change a thing to the process.

†† I found out that one of the dead giveaways of when I'm trending towards the downward slope is that I start skipping on automatically hydrating myself.

††† caffeine seems to act as a baseline offset but too much outright prevents sleep, while nicotine seems to act as a dampener, both for high and low swings of mood.