Is he thinking joyful thoughts?
These will bring a natural feeling of harmony with all things, and that is conducive to speedy sleep?
Is he thinking of how he may help others?
That is equally soothing to nerves, brain and body, and brings the refreshment of forgetfulness.
But no! the worrier has another method.

He thinks the same thoughts over and over again, without the slightest attempt to get anywhere.

He has thrashed them out before, so often that he can tell exactly what each thought will lead to.

His ideas go around in a circle like the horse tied to the wheel.

He is on a treadmill ever ascending, tramping, up, up, up and up, and still up, but the wheel falls down each time as far as he steps up, and after hours and hours of unceasing, wracking, distressful mental labor, he has done absolutely nothing, has not progressed one inch, is still in the clutch of the same vicious treadmill.