Some nights, when I lay on my bed trying to sleep but my mind is still racing, I try to calm down by counting or something that requires concentration in order to forget everything else. I noticed how I cannot count without having another train of thought talking or replaying a song I was listening to the same day. It's like having two threads running in parallel.
Trying to count visually is almost impossible, I lose track before reaching twenty. As a friend of mine put this, “I can't count sheep to sleep because they are always cheating.”
Have you tried thinking about the process of breathing ?
Ask yourself, "how do I know I am breathing?": there is some physical sensation that tells you that you're breathing, whether it's a whistling noise in your nose, the feeling of air rushing past the tip of your nose or the back of your throat, the feeling of wanting to return to the neutral position that your ribs give you during a deep breath.
For a lot of people, just one of these sensations is the most dominant one. If you can pick one, just lie quietly and concentrate on it and notice it every time you take a breath.
This process is more about noticing sensation than doing any kind of cognition, so I find it very useful when trying to take a mid-day nap (I haven't had trouble sleeping at the end of the day since I had children, funny that).
Trying to count visually is almost impossible, I lose track before reaching twenty. As a friend of mine put this, “I can't count sheep to sleep because they are always cheating.”