Table 1.

Theorised routes between nightmares and psychiatric symptoms.

Theorised pathway	Theorised mechanistic account
Nightmares to psychiatric symptoms	Nightmares act as a stressor which triggers negative affective states.
	Catastrophic nightmare related appraisals (e.g. they are a sign of bad things that are going to happen) trigger daytime negative affect and associated unhelpful behavioural responses (e.g. avoidance and hypervigilance).
	Nightmares result in insomnia, which is causally related to a range of mental health problems.
Psychiatric symptoms to nightmares	Psychiatric symptoms place greater burden on the REM sleep system, which functions to consolidate emotional memories and experiences. A dysfunction in this system results in nightmares.
	Detachment type dissociation provides short term escape from distress. Yet this prevents the opportunity for emotional processing prior to sleep. The neural underpinnings for this emotional ‘braking system’ are deactivated during REM sleep, and hence an emotionally intense nightmare is more likely to ensue.
Nightmares and psychiatric symptoms are causally unrelated	Nightmares are symptom of PTSD only.
	Nightmares are a side effect of psychiatric medication.
	Nightmares and psychiatric symptoms are both a consequence of stressful life events