Nightmares are often comorbid with other psychiatric disorders, including posttraumatic stress disorder (PTSD), insomnia disorder, psychosis, mood disorders, anxiety disorders, and grief. For this reason, nightmare disorder should be diagnosed only when the nightmares are sufficiently severe to warrant independent clinical attention. Additionally, nightmare disorder should not be diagnosed in addition to PTSD unless the nightmares are temporally unrelated to PTSD (i.e., precede the onset of PTSD or persist after the remission of PTSD).
Little is known about the neurobiology of nightmare disorder. However, some studies have linked nightmares to various neurotransmitter systems, in particular norepinephrine, serotonin, and dopamine, and to activity in affective neural networks, including the amygdala, hippocampus, medial prefrontal cortex, and anterior cingulate cortex. It is not clear if different types of nightmares (e.g., those associated with nightmare disorder versus substance use or withdrawal) share a common underlying pathophysiology. Individuals with nightmare disorder are more likely to endorse a history of adverse events, which may contribute to the incidence of nightmares.