In a 2002 study from the University of Oxford, researchers found that people who engaged in “imagery distraction” fell asleep faster than those who did not.

Insomniacs commonly complain that they are unable to get to sleep at night due to unwanted thoughts, worries and concerns... The success of the “imagery distraction” task is attributed to it occupying sufficient “cognitive space” to keep the individual from re-engaging with thoughts, worries, and concerns during the pre-sleep period.