What worked for me was regular cardio exercise and daily doses of high absorption magnesium.
The magnesium is absolutely unproven pseudoscience nonsense that can't possibly work. But if I stop taking it my sleep suffers massively.
…why?
Vitamin, mineral, and nutrient deficiencies are a very well known science.
"levels are fine" can still mean fine, too low or too high for your individual need. As long as you don't overdose, trying out a supplement nonetheless can be worth a shot, but of course it can also be a waste of money.
Unfortunately, "normal values" in medicine aren't as normal as one would like.
But realistically, very little of the $100 billion+ supplement industry is built on anything medically necessary. Yes, I have a waste basket diagnosis with an unclear cause that's helped by a specific supplement, but there are quite literally dozens (perhaps even hundreds) of other supplements that the snake oil merchants swear up and down are essential for the same condition, and they'd happily claim that whatever deficiency exists is undetectable. That's why I "don't believe" in supplements in general.
With so many systems in the body, you really have to wonder how many people actually have a _single_ issue that's causing _all_ their problems. It's much more logical that your experiences are the result of emergent phenomenon from the interaction of multiple issues. In that case, perhaps you're simply treating a secondary condition that's vastly improving the outcomes with what you view as your primary condition?
That's the good stuff. Constantly hard to find in Canada.
Edit: also this is literally the first time anyone has ever provided me with any idea if why it might actually work. So seriously, thank you for that.