One counterintuitive piece of advice I can offer is to take a cold shower right before bed. Some might think a cold shower would shock the system so much that your body would be on high alert... but that's very temporary... and when you slip into your warm bed sheets afterwards, you feel like your in a safe place.

Your milage may vary. I've seen conflicting science on this. Here is the positive case: https://www.sleepadvisor.org/showering-before-bed/