For me it was refinement. I was always an easy sleeper (> 3min i could be a sleep). But when stress piled on, it made my mind more of a clutter. So I started picturing a black background and drawing a number 1. But i had to draw the most perfect 1 I could visualize. Serifs, font what ever you want, just perfect. I would time it to my breathing. So 1 would be done in one breath (inhale and exhale). Then 2, then 3 etc.

The catch? if i had stray thoughts, i would have to start back at 1. I never get that far (101). But i always managed to clear my mind and fall asleep.

After reading about other people's techniques, it seems i stumbled on things like breathing and visualization.