Posttraumatic stress disorder (PTSD) is characterized by exposure to an extreme stressor and subsequent development of four clusters of symptoms , which include intrusive symptoms related to the traumatic event, avoidance of stimuli related to the event, negative alterations in cognition and affect and altered arousal and reactivity. The Diagnostic and Statistical Manual 5th Edition (DSM-5 ) outlines 20 possible symptoms that aid in making the diagnosis [1]. Of these 20 symptoms, only two relate specifically to sleep: the presence of distressing dreams about the event and difficulty staying asleep, falling asleep or experiencing restless sleep. Nevertheless, sleep disturbance remains among the most common symptoms and subjective complaints among people with PTSD. Patients with PTSD frequently report their sleep quality as poor. They may complain of a number of specific symptoms related to sleep including initial and maintenance insomnia, early morning awakening, nightmares and other parasomnias [2].

In this chapter, we begin by describing the scope of the sleep disturbance in PTSD. A point of distinction should be made between subjective sleep complaints (those signs and symptoms that patients express in words) and objective disturbances, which are assessed by polysomnography, actigraphy or other methods such as magnetic resonance imaging. This distinction is particularly relevant in PTSD, as studies have found varying degrees of correlation between subjective complaints and objective measures on polysomnography [3] and actigraphy [4]. Next we will characterize the various objective and subjective sleep changes that have been observed and reported in PTSD. A description of specific symptoms and objective measurement methods can be useful to the clinician or researcher who wishes to assess and treat these symptoms. Given the high degree of psychiatric and medical comorbidity that is seen in PTSD, attention will be given to sleep problems in special populations, as well as common co-occurring sleep disorders. Finally, we will provide a discussion of future directions within the assessment of sleep disturbance in this population.

Numerous studies point to a high prevalence of sleep complaints among people with PTSD. According to a community sample of adults with PTSD , over two thirds reported complaints related to sleep. An additional 40% met concurrent criteria for primary insomnia [2]. In a sample of combat veterans in the United States, 89% of eligible veterans with a confirmed diagnosis of PTSD also had a diagnosis of insomnia [5]. A community sample of 92 individuals with PTSD in Montreal, Canada, showed that sleep complaints were present in over 88% of the subjects studied [6]. Moreover, sleep quality was not associated with age, gender, marital status, the nature of the trauma or the time since the traumatic event. This finding suggests that sleep disturbance is an enduring and sensitive measure of PTSD.

There is some debate as to whether sleep disturbance is simply a secondary symptom that results from exposure to trauma or whether sleep disturbance is actually the core feature of PTSD; however, the current research mainly supports the latter hypothesis. This distinction does have clinical significance when assessing and treating the subjective sleep changes in PTSD; if sleep disturbance is a core feature of PTSD , then its assessment and treatment should be of high priority. Evidence that sleep disturbance is a core feature of PTSD arises from four main findings. First, studies have shown that poor sleep in the aftermath of exposure to trauma predicts the development of PTSD [7–9]. Second, treatment of PTSD that results in residual sleep disturbance is associated with poorer outcomes. Third, treatment that focuses on sleep disturbance improves both sleep and other features of PTSD [10, 11]. Fourth, neuroimaging studies have demonstrated that brain regions impacted by sleep disturbances share large overlap with regions known to be associated with PTSD [12]. At this time, we cannot definitively conclude that sleep is the hallmark feature of PTSD, but we can argue that sleep disturbance is prevalent in patients with PTSD and it certainly merits assessment and treatment. Further research continues in this area.

Although sleep disturbance is a common feature in patients with PTSD, it is important to note the heterogeneity that exists within the diagnosis [5]. Factors that influence the presentation of PTSD include, but are not limited to, (1) the nature, severity and duration of the trauma, (2) the developmental level of the individual affected, (3) the past personal and psychiatric history of the individual affected and (4) the resources and supports available to individuals.

Insomnia is perhaps the most widely reported symptom in PTSD [2]. Insomnia is defined as the inability to initiate or maintain sleep and may encompass elements of non-restorative sleep, i.e. sleep that is considered non-refreshing. All three types of insomnia (initial, maintenance and non-restorative sleep) have been reported in patients with PTSD. The underlying pathophysiology may relate to a constant state of hyperarousal, both physiological and cognitive, which interferes with sleep functioning. It may be perpetuated by maladaptive sleep behaviours that individuals with PTSD adopt to deal with their symptoms (e.g. avoidance of sleep, alcohol use). Chronic insomnia (insomnia of duration greater than 1 month) is clinically significant, as it is associated with increased healthcare use, hypertension, diabetes and mortality [13, 14].

There is ample evidence of sleep disturbance in PTSD following exposure to military combat . One recent study found that 41% of returning service members from Iran and Afghanistan reported insomnia. These initial reports of insomnia were predictive of PTSD at follow-up [15]. Other studies have also shown that insomnia is one of the most common complaints of veterans returning from Operation Enduring Freedom/Operation Iraqi Freedom post-deployment [16]. Based on data from the National Vietnam Veterans Readjustment Study – a large study of veterans who served during the Vietnam War – rates of sleep disturbance are exceedingly high; 44% of veterans with PTSD reported difficulties initiating sleep, and 90% reported difficulties maintaining sleep [17]. In this study, combat exposure was correlated with sleep symptoms, including insomnia and nightmares. Service members returning from military deployments may be reluctant to report other symptoms of PTSD due to stigma; sleep complaints and insomnia may be a more accepted complaint for which one can seek treatment.

Insomnia is found in other types of trauma as well. A study of Holocaust survivors found that although only 3.8% met full criteria for PTSD, sleep disturbance rates reached 62%, a rate significantly higher than the control group [18]. This effect held even after controlling for age, education, religious observance and past-year presence of anxiety and depressive disorders. The significance of this finding is that sleep disturbance can remain long after exposure to trauma and that sleep disturbance may persist even after the other symptoms of PTSD have resolved or when symptoms do not meet full diagnostic criteria for PTSD.

Natural disasters such as hurricanes or earthquakes may precipitate PTSD in both children and adults. For example, studies of children who have survived hurricanes have shown significant rates of sleep disturbance and nightmares. In a study looking at a cohort of children following Hurricane Hugo, 35% of children endorsed sleep difficulties and 9% endorsed nightmares. The sleep difficulties were most prominent in children of a younger age, suggesting that developmental stage does mediate the emergence of sleep symptoms [19]. Another study examined children in the aftermath of Hurricane Katrina and found high rates of PTSD, with specific symptoms of difficulty initiating sleep and fear of sleeping alone. Sleep disturbances were more pronounced in women, those of a younger age and those whose lives continued to be disrupted by the disaster [20].

There is a clear connection between childhood sexual abuse and the development of PTSD. Childhood sexual abuse is correlated with insomnia and nightmares, both with and without comorbid PTSD. One hypothesis that may explain this link is that sleep naturally occurs in a place of safety and security. For victims of childhood sexual abuse, both the bedroom and the night (both the place and the time during which abuse frequently occurs) become associated with fear, thereby limiting sleep. A further consequence of insomnia in this population has to do with the long-term effects of chronic insomnia; adolescents who do not have restorative sleep may experience daytime sleepiness, more emotional dysregulation and difficulties processing unsafe or dangerous situations. Such a state of sleep deprivation may make them more vulnerable to future re-victimization [21]. See the case vignettes at the end of this chapter for relevant clinical examples.

Nightmares are a common subjective complaint in patients with PTSD, reported by 19–71% of PTSD patients [10, 22], which can persist for many years following exposure to trauma [8], even after the completion of treatment for PTSD [10]. Nightmares can be understood as part of the re-experiencing process seen in PTSD. Nightmares can be defined as “a frightening dream that awakens the dreamer from sleep” [23]. There is controversy over the necessity of the dreamer awakening from sleep in order to define a nightmare, as many people describe disturbing dreams in the absence of awakening; some may only recall the emotional elements (e.g. fear, sadness, dysphoria) that have occurred in the context of a nightmare. The International Classification of Sleep Disorders II captures this distinction by defining nightmares as disturbing mental experiences rather than frightening dreams [24].

Nightmares may awaken an individual from sleep with varying degrees of recall and can be quite distressing to the affected individual. Even if the exact content is not recalled, the emotional elements may be present, such as fear, distress and entrapment. The nightmares may be exact replicas of the scenarios or contain varying degrees of symbolization, emotional content and autonomic arousal [8].

Dreams serve an important function after exposure to trauma, specifically in the integration and processing of highly emotional content. Thus, dreams and nightmares may initially be considered as a means of adapting to trauma and integrating it within the psyche. However, the persistence of nightmares months or years after trauma conceptualizes PTSD as a disorder of failed adaptation and/or trauma that overwhelms an individual’s coping mechanism. There is conflicting evidence as to whether dream recall is heightened or impaired after exposure to trauma, again reflecting the heterogeneity of the disorder. Some patients report vivid recalls of nightmares, and others report only awakening in a state of panic, without recall of the actual content. In some patients, dream recall may be initially quite vivid, with a gradual decrease over time and with adaptation to the trauma.

The actual content of nightmares can provide useful information in understanding the patient and their traumatic experience (though appropriate caution must be taken when bringing up traumatic memories, especially in the absence of desensitization or other appropriate therapeutic treatments). Most researchers classify nightmares according to the degree to which they are similar to the trauma experienced by a person. Nightmares may be classified as posttraumatic, modified or disguised, based on their content. Posttraumatic dreams are those that involve content of the actual trauma experienced. A veteran who dreams of actual events he/she experienced during the war would fit in this this category. Modified dreams present content that is not directly related to the trauma, but is closely related. Finally, disguised dreams use symbols, images and emotions to replay the traumatic content [25]. Dreams with posttraumatic content are more prevalent early after exposure to trauma, and ongoing posttraumatic dreams are associated with a higher degree of PTSD. Dreams are more likely to be set in the past in patients with PTSD. A higher level of dream recall and recurrent nightmares is also associated with more symptoms and persistence of PTSD as well as poorer clinical prognosis [8].

One study of World War II veterans and civilians exposed to war found posttraumatic nightmares in 102 out of 124 people with PTSD [26]. Forty-two percent of these nightmares were posttraumatic in nature; that is, their content was replicative of the events experienced. Twenty-eight percent were non-replicative and 35% were a mixture of replicative and non-replicative content. Posttraumatic nightmares that were replicative in nature were associated with fewer hours of sleep, greater fear of going to sleep, depression upon waking and greater PTSD symptom severity. As well, those with replicative posttraumatic nightmares showed a greater frequency of nightmares. Thus, the degree of similarity between the nightmare content and the actual trauma is associated with a higher degree of symptom severity and comorbidity.

Mellman et al. [27] examined 60 patients with exposure to trauma and created dream reports by having patients keep a morning diary to remember their dreams. Thirty percent of these patients were able to remember a dream. Of these, half the dreams contained content related to the trauma. Almost 50% were dreams that closely resembled the traumatic event, while the remainder were either distressing in emotion alone or neutral. Those who experienced trauma dreams were more likely to go on to develop PTSD.

Patients who experience nightmares may actively engage in sleep avoidance . This may take the form of poor sleep hygiene, using stimulants at bedtime, or reversal of circadian rhythms. Sleep avoidance can create further impairments for patients with PTSD as it may worsen mood symptoms, lead to daytime sleepiness and worsen emotional dysregulation in the context of sleep deprivation. Sleep deprivation may also make individuals less able to access resources and support and re-engage in meaningful activities that would otherwise be helpful in coping with trauma.

Nocturnal panic is another subjective sleep complaint that may present in patients with PTSD [28, 29]. Nocturnal panic is defined as the awakening from sleep in a state of panic. A panic attack consists of both cognitive and physiological responses, usually involving fear or discomfort, along with accompanying somatic or cognitive symptoms. Symptoms of a panic attack may include palpitations, sweating, trembling or shaking, shortness of breath, choking, chest pain or discomfort, nausea, feeling dizzy, derealization, fear of losing control or dying, paraesthesias, chills or hot flashes. Diagnostically, four of the above criteria are required to meet criteria for a panic attack [1].