When I'm having nightmares lately I know it is because my unconscious mind is sorting things out. Whenever I'm going through a shift, I have a few days (nights) of nightmares.
If I'm fighting against them, trying to make them not happen, or keep the fear with me during the day.... they continue longer.
If I just accept them as gunk that my unconscious mind is sorting out, they go away sooner.
Maybe this resonates with you?