The causes of nightmares
Alexandre Lemyre, M.A., Ph.D.
The content of this article was last updated on February 1, 2022.
Introduction
Better understanding the causes of nightmares is a fascinating endeavor, and I believe that it is a necessary step toward improving psychological treatments for this sleep problem. In 2015, in the context of a research internship, I developed and conducted a qualitative study on the perceptions of nightmare sufferers in relation to their nightmares. The article reporting the results of this study was finally published a few years later (Lemyre et al., 2019); yes, research can take time! I will come back to this study at the end of this post, as it contains interesting findings on the perceptions of nightmares sufferers regarding the causes of their nightmares. All in all, conducting this research led me to deep dive in the scientific literature on the causes of nightmares, and I kept up to date since then. In this post, I will summarize the state of research on this topic.
Posttraumatic nightmares as a result of traumatic experiences
The most obvious cause of nightmares is the experience of traumas. Among individuals who develop a posttraumatic stress disorder following a traumatic experience, about two thirds suffer from posttraumatic nightmares (Milanak et al., 2019). A posttraumatic nightmare is a nightmare for which the theme, setting, content or main emotion share some similarity with a past traumatic experience (Duval & Zadra, 2010).
What exactly is a traumatic experience? The American Psychiatric Association (2022) defines traumatic experiences as an “Exposure to actual or threatened death, serious injury, or sexual violence.” The traumatic event can be experienced directly, witnessed, or learned (for instance, learning that a relative has committed suicide). For some workers, such as first respondents (e.g., police officers, paramedics) and children service protection workers, repeated exposure to the aversive details of traumatic events (e.g., collecting human remains after an accident, being exposed to reports of child abuse) can also constitute a traumatic experience. Exposure to traumatic events through the media is not considered to be a traumatic experience (American Psychiatric Association, 2022). One of the most widely used scales for evaluating exposure to traumatic events is the Life Event Checklist (Gray et al., 2004) developed by the National Center for PTSD in the United States. The following traumatic experiences are listed in this questionnaire, and each of them is susceptible to result in posttraumatic nightmares:
- Natural disaster (for example, flood, hurricane, tornado, earthquake)
- Fire or explosion
- Transportation accident (for example, car accident, boat accident, train wreck, plane crash)
- Serious accident at work, home, or during recreational activity
- Exposure to toxic substance (for example, dangerous chemicals, radiation)
- Physical assault (for example, being attacked, hit, slapped, kicked, beaten up)
- Assault with a weapon (for example, being shot, stabbed, threatened with a knife, gun, bomb)
- Sexual assault (rape, attempted rape, made to perform any type of sexual act through force or threat of harm)
- Other unwanted or uncomfortable sexual experience
- Combat or exposure to a war zone (in the military or as a civilian)
- Captivity (for example, being kidnapped, abducted, held hostage, prisoner of war)
- Life-threatening illness or injury
- Severe human suffering
- Sudden violent death (for example, homicide, suicide)
- Sudden accidental death
- Serious injury, harm, or death you caused to someone else
- Any other very stressful event or experience
It is worth noting that traumatic experiences do not systematically produce posttraumatic nightmares. About one out of ten individuals exposed to a trauma will eventually develop a posttraumatic stress disorder (PTSD; Breslau, 2009). Among individuals with a PTSD diagnosis, about two out of three experience posttraumatic nightmares (Melissa E Milanak et al., 2019). Of course, it is also possible to experience posttraumatic nightmares without fulfilling all other clinical criteria for PTSD.
Traumatic experiences that are perceived as more severe often result in posttraumatic nightmares that are more similar to the actual traumatic experience (i.e., more replicative). Moreover, as a rule, the similarity between the traumatic experience and the posttraumatic nightmares tends to decrease over time (Duval & Zadra, 201022).
The relationship between neuroticism and nightmares
Neuroticism is one of the Big-Five personality traits, along with openness to experience, conscientiousness, extraversion, and agreeableness. Neuroticism is defined as a tendency to experience negative emotions. Most (but not all) studies report a positive relationship between neuroticism, nightmare frequency and nightmare distress (Kelly et al., 2018; Lancee et al., 2010; Schredl & Goeritz, 2019; Spoormaker et al., 2006 for a review). This means that individuals who tend to experience more negative emotions (i.e., individuals who are higher in neuroticism) also tend to experience more nightmares, and to experience more negative consequences from their nightmare problem. Schredl and Göritz (2020) found that an increase in neuroticism over the course of two years was associated with an increase in nightmare frequency, whereas a decrease in neuroticism over the same period was associated with a decrease in nightmare frequency. One hypothesis to explain these results is that experiencing negative emotions increases the risk of experiencing nightmares, either directly or indirectly. There might also be a bidirectional relationship, whereas the experience of negative emotions favors nightmares, which in turn increase emotional reactivity to negative events.
The perceptions of nightmare sufferers regarding the causes of their nightmares
One obvious way to learn about the possible causes of nightmares is to directly question nightmare sufferers. In this section, I present studies that have used this approach, from the oldest to the newest.
In a study by Dunn and Barrett (1988), thirty-six undergraduate students who experienced at least four nightmares per month were administered a questionnaire containing possible causes of nightmares. The percentage of participants endorsing each cause was as follows: school or job pressure (64% of the participants), conflicts in important relationships (44%), bad news (35%), recent frightening experience such as watching a frightening movie (29%), and illness and unusual tiredness (24%).
In a study by Thünker et al. (2014), 335 individuals with an average of 12 nightmares per month were administered a questionnaire containing possible causes of nightmares. Contrary to the first study by Dunn and Barrett, participants were asked to report the possible causes of nightmares in general, not necessarily referring to their own nightmares. While raw numbers are not reported, we can eyeball the bar graph and conclude that nightmares were attributed to stress (≈ 80% of the sample), inner conflicts (≈ 80% of the sample), traumas (≈ 77% of the sample), personality (≈ 34% of the sample) and genes (≈ 8% of the sample).
In a study by Cohen and Zadra (2015), 581 individuals (including undergraduate students and individuals from the general population) reported their worst nightmare, as well as a description of the presumed cause of this nightmare. The authors used a grid of 11 possible causes of nightmares (which they built based on the scientific literature) to categorize the participants’ descriptions. Overall, the participants attributed their worst nightmare to interpersonal relationships (18.1% of the participants), entertainments such as movies or videogames (9%), death of others or fear of death (8.1%), specific phobias (defined loosely as non-relational fears; 8.1%), negative emotions and states, including fatigue and physical discomfort (7.9%), difficulty with physical or mental health (6.4%), spiritual or paranormal causes (5.2%), a significant event or situation, including a past trauma (4.8%), the physical environment (4.5%), and helplessness, insecurity or self-discovery (5.5%). I omitted three categories (“others”, “no origin”, and “unknown”), which is why the total does not reach 100%. Interpersonal relationship was by far the most reported cause, and it could refer to conflicts into a relationship, the absence of a loved one, fear of a loved one getting hurt or fear of a relationship ending (Cohen & Zadra, 2015).
In our own study (Lemyre et al., 2019), I interviewed 20 university students who experienced a nightmare problem ranging from mild to severe (i.e., several times per week for several months). For many participants, the frequency of nightmares had varied substantially during the past year. As part of the interview with the participants, I asked them what they believed had caused their nightmares. We then analyzed the interviews and created categories based on the participants’ answers. Here is what we found (in parentheses, I report the number of participants who reported each cause):
- Occupational causes, including stress related to school (12 participants) and work (6 participants).
- Interpersonal issues, including separations (12 participants), relational difficulties (8 participants), fear of the actions of others (4 participants), and solitude or isolation (4 participants).
- Psychological traits, including a tendency to experience anxiety (4 participants), fear of rejection (3 participants) or a low self-esteem (2 participants).
- Physiological causes, including the intake of medication (2 participants) or melatonin (2 participants), or eating before bedtime (2 participants).
- Negative emotions that do not have a clear cause, including stress (10 participants) and fears (3 participants).
- Significant life events, including events that threatens life (such as a car accident; 4 participants), events that do not threaten life (such as an abortion; 3 participants), and prolonged events that do not threaten life (such as instability at a young age; 2 participants).
- The use of screen-based electronics before bedtime (5 participants)
- The anticipation of negative events (4 participants)
- Self-destructive behaviors (such as drug use or self-harm; 3 participants)
- A perceived lack of control (3 participants).
Summary and Conclusion
The causes of nightmares could be manifold. These include traumatic experiences (for posttraumatic nightmares) and neuroticism, defined as a tendency to experience negative emotions. When questioning nightmare sufferers about the perceived causes of their own nightmares (or the perceived causes of nightmares in general), a high level of stress is often reported, especially, stress in relation to significant relationships or professional activities (work, studies). As a rule of thumb, it is generally accepted by dream researchers that there exist a continuity between concerns in waking (which may be positive or negative) and the content/emotions of dreams (Domhoff, 2011; Hartmann, 2011; Schredl, 2015), with the implication that negative concerns may lead to dysphoric dreams and nightmares.
References
American Psychiatric Association. (2022). The Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-5-TR). Author.
Breslau, N. (2009). The epidemiology of trauma, PTSD, and other posttrauma disorders. Trauma, Violence, & Abuse, 10(3), 198-210. https://doi.org/10.1177/1524838009334448
Cohen, A., & Zadra, A. (2015). An analysis of laypeople’s beliefs regarding the origins of their worst nightmare. International Journal of Dream Research, 8(2), 120-128. https://doi.org/10.11588/ijodr.2015.2.20328
Domhoff, G. W. (2011). Dreams are embodied simulations that dramatize conceptions and concerns: The continuity hypothesis in empirical, theoretical, and historical context. International Journal of Dream Research, 4(2), 50-62. https://doi.org/10.11588/ijodr.2011.2.9137
Dunn, K. K., & Barrett, D. (1988). Characteristics of nightmare subjects and their nightmares. Psychiatric Journal of the University of Ottawa, 13(2), 91-93.
Duval, M., & Zadra, A. (2010). Frequency and content of dreams associated with trauma. Sleep Medicine Clinics, 5(2), 249-260. https://doi.org/10.1016/j.jsmc.2010.01.003
Gray, M. J., Litz, B. T., Hsu, J. L., & Lombardo, T. W. (2004). Psychometric properties of the life events checklist. Assessment, 11(4), 330-341. https://doi.org/10.1177/1073191104269954
Hartmann, E. (2011). The nature and functions of dreaming. Oxford University Press.
Kelly, W. E., Mathe, J. R., & Yu, Q. (2018). Specific versus scaled estimates: A comparison of two approaches to measuring retrospective nightmare frequency. International Journal of Dream Research, 11(2), 203-206. https://doi.org/10.11588/ijodr.2018.2.48486
Lancee, J., Spoormaker, V. I., & Van Den Bout, J. (2010). Nightmare frequency is associated with subjective sleep quality but not with psychopathology. Sleep and Biological Rhythms, 8(3), 187-193. https://doi.org/10.1111/j.1479-8425.2010.00447.x
Lemyre, A., St-Onge, M., & Vallières, A. (2019). The perceptions of nightmare sufferers regarding the functions, causes, and consequences of their nightmares, and their coping strategies. International Journal of Dream Research, 35-48. https://doi.org/10.11588/ijodr.2019.2.62396
Milanak, M. E., Zuromski, K. L., Cero, I., Wilkerson, A. K., Resnick, H. S., & Kilpatrick, D. G. (2019). Traumatic event exposure, posttraumatic stress disorder, and sleep disturbances in a national sample of U.S. Adults. Journal of Traumatic Stress, 32(1), 14-22. https://doi.org/10.1002/jts.22360
Milanak, M. E., Zuromski, K. L., Cero, I., Wilkerson, A. K., Resnick, H. S., & Kilpatrick, D. G. (2019). Traumatic event exposure, posttraumatic stress disorder, and sleep disturbances in a national sample of US adults. Journal of Traumatic Stress, 32(1), 14-22. https://doi.org/10.1002/jts.22360
Schredl, M. (2015). The continuity between waking and dreaming: Empirical research and clinical implications. In M. Kramer & M. Glucksman (Eds.), Dream research: Contributions to clinical practice. (pp. 27-37). Routledge/Taylor & Francis Group.
Schredl, M., & Goeritz, A. S. (2019). Nightmare frequency and nightmare distress: Socio-demographic and personality factors. Sleep Science, 12(3), 178-184. https://doi.org/10.5935/1984-0063.20190080
Schredl, M., & Göritz, A. S. (2020). Stability of nightmare frequency and its relation to neuroticism: A longitudinal study. Journal of Sleep Research, 1-5. https://doi.org/10.1111/jsr.13126
Spoormaker, V. I., Schredl, M., & van den Bout, J. (2006). Nightmares: from anxiety symptom to sleep disorder. Sleep Medicine Reviews, 10(1), 19-31. https://doi.org/10.1016/j.smrv.2005.06.001
Thünker, J., Norpoth, M., von Aspern, M., Özcan, T., & Pietrowsky, R. (2014). Nightmares: Knowledge and attitudes in health care providers and nightmare sufferers. Journal of Public Health and Epidemiology, 6(7), 223-228. https://doi.org/10.5897/JPHE2013.0565
