I like to think about scifi stuff when I can't sleep and someone recommended audio books in one of the comments. There is a podcast by Isaac Arthur about science and futurism, and he provides narration only versions. Honestly this is a miracle for my sleep.

It's very interesting and because it doesn't have music and loud sounds it will not wake you up if you fell asleep.

https://soundcloud.com/isaac-arthur-148927746a

(I think there is a bug in soundcloud where the RSS feed does not show past a few tens of older episodes? Not sure where to get all of them)

I think you can import the URL into your podcast reader.

Same with me. I start to think fiction and then I kind of blur the line between a dream and my thinking and just falling asleep.