The best thing I’ve found for insomnia, other than medication/melatonin, is imagining myself flying. Basically going to silly fantasy land bootstraps a sleep state pretty reliably.
I try and build little worlds in my head and fly around them, working on adding details as I go. I think it works because it blocks everything out and requires zero physical effort.
It’s usually flying for me as well. It’s just interesting enough to not be too Beijing. But it’s completely independent of what happened during the day, will tomorrow, etc.
Can you not? Like as in you have aphantasia and can't picture things, or you just don't readily imagine stuff? Because if it's the first one I'm sorry for you, but in the second case it is something you can practise.
I listen to BBC radio dramas - ones that aren't too dramatic. I usually manage to get in about 10 minutes before I fall asleep. Either that or the 531 podcast.
I used to spend a lot of time flying and, thankfully, I've always found it easy to sleep on planes.
However, a few years back a colleague was building a server on a desk near me and it sounded very like the inside of a plane and I became very drowsy almost immediately!
