Earlier quoted context omitted.
This reminds me of an anecdote from Feynman about what sorts of mental things he could and could not do while counting seconds, and how it was different for different people. His counting was internally verbal and he could do anything that didn't require him to speak or anything else that was internally verbal. On the other hand, a mathematician he knew was able to do lots of mental things while counting that Feynman…
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…
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"mind racing before sleep"? If you smoke, try not to smoke at least 1 hr before you go to bed.