Suicide, which is the first cause of death among young people, is associated with several modifiable or non-modifiable risk factors, so it is important to be able to identify and manage [17]. Nightmares have been identified as one of the modifiable risk factors for suicide, with specific treatments, such as Image Rehearsal Therapy or Systematic Desensitization and Progressive Deep Muscle Relaxation training for treatment of idiopathic nightmares, or Prazosin if nightmares are associated with of Posttraumatic Stress Disorder (PTSD) [58,60]. Furthermore, as mentioned above, nightmares may be associated with early stages of psychotic or mood disorders, and its treatment may prevent the conversion to a full psychiatric disorder.

This work clearly emphasizes a need to use standardized definitions of nightmares across studies, as we observed a lack of consensus criterion. Indeed, “frequent nightmare” was differently defined from one study to another, and sometimes not defined at all. With our code with asterisks (from * to **** when no definitions were proposed, see our methods), we tried to clarify this issue. We plead for standardized use of either the DSM-5 definition or systematic use of published questionnaires such as the Mannheim Dream Questionnaire (MADRE) [60]. DSM-5 defines a mild nightmare disorder as less than one episode per week on average, a moderate disorder as one or more episodes per week, but less than nightly, and a severe disorder as nightly episodes. An acute episode has a duration of 1 month or less, a sub-acute episode a duration between 1 to 6 months, and chronic nightmares endure for 6 months or longer (APA, 2013). Instruments to assess nightmare frequency and nightmare distress exist such as the Nightmare Frequency Questionnaire (NFQ) [61] or the MADRE [60]. The use of such instruments should be more generalized.

 

Some caveats and limitations of the existing scientific literature reviewed here should be emphasized. First, most studies of nightmares and mood disorders [62] assessed major depressive disorders (MDD), without any information about the unipolar of bipolar subtype of depression. This could bias results; for example, Marinova et al. [22] found a difference in the frequency of nightmares between unipolar and bipolar depression. Patients with unipolar depression and nightmares were more likely to have suicidal thoughts than those without nightmares; this difference was not found in patients with bipolar disorder (although this was a smaller group with underpowered statistics). Second, patients with PTSD or recent trauma were either not screened, nor always excluded from the studies. Yet nightmares are one of the mains symptoms of PTSD and stress-related disorders. This may have been a confounding factors in reported studies [46,48]. Third, there was no information of comorbid personality disorders; as in PTSD it may have been a confounding factor, as it is known that some personality disorders such as borderline personality are more associated with nightmares [2]. Fourth, most cohort studies examined the frequency of nightmares in their patients and looked for an association with suicidality. A significant majority did not report information on the severity of psychiatric symptoms. Patients who had more frequent nightmares were more likely to have suicidal thoughts or attempts but may also have had a higher intensity in their symptoms, which may have led to higher suicidality. Fifth, there was little information about the distinction between bad dreams/nightmares in reported studies. Nightmares are different from bad dreams since nightmares awaken the sleeper [10]. Sixth, only few studies mentioned their patient medication. However, nightmares have been found as being a side effect of some antipsychotics and antidepressant treatments, and so may have been a confounding factor as well [63]. Finally, all the studies were based on clinical evaluation (self-report nightmares or clinician interview), which can have led to a memory bias. There were no laboratory examinations of nightmares with more objective measures (except in the study of Lusignan et al. [40], who explored dreams and not nightmares).