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Nightmare in REM Sleep: How Stress Affects the Content of Our Dreams

By Katharine Santiago

Have you ever wondered why you dream about falling into a never-ending hole, or about all of your teeth falling out? What does this say about who you are or your subconscious thoughts? Researchers have begun to hypothesize that dreams can actually say quite a bit about how stressed you are. There is some research on trauma-related nightmares in those who suffer from Post-Traumatic Stress Disorder ( PTSD), a psychiatric disorder caused by a traumatic event in one’s life. However, we do not know much about other kinds of nightmares that have no known triggers.

Some nightmares, called idiopathic nightmares, occur as a result of stress or physical illness. They are most common in middle childhood (defined by developmental psychologists as ages 6-12), as well as during rapid eye movement (REM) sleep. Characterized by rapid movements of the eyes (hence the name) and vivid dreams, REM sleep is one of the phases of the sleep cycle (Davis, 2014). These bad dreams can occur at any age, and we don’t quite know why at this time, but it’s a question worth exploring. We have all experienced a few dreams with some strange story-lines that may even be terrifying at times, and for those of us who are curious, we seek to understand why.

A study done at the University of Montreal in 2003 recruited students who reported having one or more nightmares per week for six months. If these participants reported these nightmares occurring after a traumatic event, PTSD status was determined by a clinical assessment. Results of this study showed that those with PTSD who have frequent nightmares are affected differently than those who experience idiopathic nightmares. These participants reported more nocturnal awakenings, which indicates that sleep in PTSD patients can be characterized by a lower arousal threshold (they can be woken up more easily). This resulted in lower sleep efficiency in these patients as well. While this study mainly revealed information on the abnormal processes of sleep in PTSD patients, it also was important in understanding the brain activity that correlates to idiopathic nightmares as well, including the possible system dysfunctions that lead to intense dreams that may be negative or peculiar for some (Germain & Nielsen, 2003).

There’s one theory that suggests our dreams reflect the process of memory consolidation and help to integrate our new knowledge and experiences with the old. During the process of memory consolidation, our brain changes in a way that allows us to encode and physically store memories. In order for this to occur, multiple areas of the brain and many neurotransmitters must interact. Researchers at the University of Arizona specifically focused on cortisol, or “the stress hormone”, and how it influences the memory consolidation process that occurs while we sleep. REM sleep is important in the consolidation of procedural memories, or memories relating to the process of how we get things done. This research has made the assumption that dreams reflect activities in the brain related to processing and storing recent experiences. The researchers hypothesized fragmented story lines and “bizarre” imagery in our dreams reflect disrupts communications between the hippocampal and neocortical regions of the brain. When we sleep, neocortical structures, (which relate to higher functions of the brain, including conscious thought), normally communicate with the hippocampus to enhance retrieval of memories and allow us to remember key details of recent events. But when cortisol levels rise in response to stress, this disrupts hippocampal functioning, and as a result this affects processing and storing. So then fragments of memory are activated in isolation, and are composed into a story by our brain with certain themes, therefore creating a dream. The nature of these dreams is very similar to that of our memories created during times of stress, which also tend to be fragmented (Payne & Nadel, 2004). Our brain puts them together as a story because there is a need for order and a sense of meaning that may not exist at all.

A different study done at the University of Montreal in 2014 collected 9,796 dreams, with 253 of them being nightmares and 431 bad dreams. The researcher’s goal was to analyze the content of nightmares and bad dreams, with a broader applicability to understanding the causes and prevalence of nightmares. Theme was one of the aspects of the dream that was analyzed. Physical aggression was most common in the nightmares, while interpersonal conflict was most common in bad dreams. They also found that nightmares were more likely to have two themes, whereas bad dreams usually had only one. Bad dreams were also more likely to be emotionally intense, which was one of the more significant findings from this study. They also looked at the narratives to clarify how and why these bizarre stories turn into bad dreams or nightmares (which were described by participants as more bizarre and negative in content). This change was initiated by either a negative event, cognition, or emotion (Robert & Zadra, 2014).

There has been plenty of research on trauma-related sleep disturbances, but not much is known about idiopathic nightmares or why they occur. Hopefully this and other past studies will bring more attention to sleep disturbances that affect people regardless of what disorders they may suffer from, including PTSD. Research like this is intended to expand our understanding of sleep and how the brain functions during it to produce dreams, but it can be applied more broadly to help further classify sleep disorders and figure out when nightmares cause significant distress and impairment and how to reduce it. There are some interesting theories as to why we dream about what we do and why sometimes our dreams are negative in content, and this allows us to question human behavior and further build upon our knowledge of it through research. Not only that, but if sleep is a time for memory consolidation, and our dreams reflect when this process is faulty, this can have larger implications that can teach us something about memory and how to improve it, or use our bad dreams to come up with new ideas in a waking state. Losing all your teeth may scare you, but next time you have a strange dream, think about what stressors in your life could be responsible. Just don’t get too scared by those either.


Nielsen, T. A., & Germain, A. (2003, April 26). Sleep pathophysiology in posttraumatic stress disorder and idiopathic nightmare sufferers. Retrieved from

Payne, J. D., & Nadel, L. (2004). Sleep, dreams, and memory consolidation: the role of the stress hormone cortisol. Retrieved from

Robert, G., & Zadra, A. (2014, February 1). Thematic and content analysis of idiopathic nightmares and bad dreams. Retrieved from

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