Eye Movement Desensitization and Reprocessing (EMDR) is a psychotherapy treatment that was originally designed to alleviate the distress associated with traumatic memories (https://www.emdr.com/what-is-emdr/). However, it is shown it can be used to alleviate other symptoms.
It has been shown that eye movements of other forms of bilateral stimulation seem to activate your problem solving process, something that happens during rapid eye movement sleep (REM) when you are darting your eyes back and forth.
By focusing on a specific problem, and both its negative and positive emotions, sensations, and beliefs, then adding bilateral stimulation, or engage in using vibrating tappers that you old with your hands, your brain begins problem solving.
Since you are focusing on the specific problem, your brain is able to work through it more effectively than what would happen if it randomly comes up while you are sleeping.
For more information on EMDR please visit the EMDR Institute: https://www.emdr.com/