This is going to sound corny as shite but I find that it helps a lot. When I can't stop thinking about things I'll choose to redirect my thoughts and basically start daydreaming in bed. I have two scenarios that I've found help (in the same way counting down from 100 does before surgery...I'll be thinking and suddenly I'm waking up in the morning). One is I'll imagine I have some superpower or something and sometimes I just think about what it would be like saving people from disasters and stuff, but for fun I usually imagine what it would be like if I were, say Superman, and
Earth was a place where monsters and evil creatures really existed.
So one night I might be getting stalked by a werewolf in the woods, and I imagine as many details as possible down to the bark of the trees, temperature, mist, how the ground feels (it helps eat up your mental resources) and eventually I'll have my little confrontation with the werewolf during which he learns that you do not frick with Superman. Michael Myers, Jason, vampires...they've all learned the same lesson.
Another scenario I find fun has to do with the Predator (like the "Get to the choppa" Predator) because that's been my favorite movie/creature since I was little. I'll imagine the same scenario only instead of "starring" I watch the events unfold. So now you might have a werewolf hunting some poor schmuck only you now have a fricking Predator hunting the werewolf, which often leads to amusing scenes because I like to offer commentary, "You think you're so terrifying Mr. Wolf...just wait until you see what's coming to frick you up."
Childish? Yep. Laughable even? Probably. But it's also a hell of a lot of fun and really keeps my mind occupied, and here's the trick, without me focusing on keeping my mind occupied/non-occupied. I get so that I'm no longer aware of the thoughts in my head and so I don't have a thousand of them on repeat and that allows me to relax and eventually drift off. Laugh if you want, but give it a try (or something similar) and it might just help.