I prefer a high-CBD strain of cannabis, shuts me right off. Similar to what has been used to treat seizure disorders. Unfortunately it's illegal basically everywhere, but I'm moving to Colorado in a few months so, yaaaay. I won't even have to get diagnosed/prescribed to legally ingest it, and I can freely grow my own. And once I run out my schedule goes haywire, 36 hours up and 12 hours sleeping (eventually, you will pass out regardless what your brain wants, but that is nearly painful).
Also quitting caffeine helped calm it down but that is nearly impossible (almost everything has trace amounts, chocolate, "decaf" coffee, and it can be a tedious effort in itself to track and avoid them), as if you don't go cold-turkey and stick to 0% intake (and then wait weeks for metabolites to rebalance, and suffer the terrible headaches/withdrawal) it does no good at all. But once I was caffeine-clean many of my sleep and exhaustion issues disappeared. Eventually I got tired of sleeping so much so I snuck some back in, and now I'm on like 2 cases of Redbull a week, and get crappy sleep all the time. Eventually I get so tolerant of the caffeine that simply not drinking another can will lead to passing out within the next hour. I'll get so tired that I feel like I'm about to fall over but still won't be able to actually sleep, after a certain point I "missed the sleep train" and have to wait. Beer also works, but I have to pass out at the right point of the come-down or again, I miss the "sleep train".
Melatonin works OK but it doesn't shut down the background thought noise at all. Ambien worked pretty good, but I'm not much of a fan of mass produced drugs, especially ones I may become dependent on. Meditation can work, breathing exercises, going to a "comfortable space" in your mind's eye, all of that, but I generally don't have an hour before sleep to focus on getting ready for sleep. It's usually quite suddenly 4am (because I wasn't staring at the clock) and I have to be up at 8am.