I used to have the same sleep problem (head won't stop racing), and mindfulness exercises throughout the day have greatly improved things for me. In a way it feels like the ability to turn it down for a time, long enough to get so tired it doesn't start back up again.

One trick I found myself is to visualise things in the noise from your closed eyes. Try to interpret something you can vaguely see, and then try to visualise it. This imposes a kind of clear image for a short duration for me, from which I try to see and visualise something else in there and so on, kind of like a visual association chain. That really gets me sleepy after a couple of minutes!