A bit dry and dusty, but Hartmann's research into nightmares found a heightened level of nightmares in artistic (and schizo-susceptible) people, who are more likely in general to be introspective, "sensitive" and have "permeable boundaries" in various neurological and social ways. He also found (similar to reality breaks in schizophrenics) that doses of dopamine could increase nightmare intensity and frequency -- the opposite was also true: anti-psychotic dopamine blockers dampen nightmares.