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Volume 14 No. 12
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Accepted Papers

Letters to the Editor

Further Exploring the Associations Between Sympathetic Activation, Fear of Sleep, and Insomnia Symptoms in Posttraumatic Stress Disorder

Jennifer C. Kanady, PhD1,2,3; Shira Maguen, PhD1,2; Thomas C. Neylan, MD1,2
1San Francisco VA Health Care System, San Francisco, California; 2Department of Psychiatry, University of California, San Francisco, California; 3Mental Illness, Research, Education, and Clinical Center, San Francisco, California

In their letter, Dr. Gupta and Ms. Sheridan provide further evidence supporting the idea that fear of sleep is associated with indices of hyperarousal during wakefulness and sleep in individuals with posttraumatic stress disorder (PTSD).1 Gupta and Sheridan examined the association between fear of sleep, PTSD symptoms, and sleep characteristics in 40 civilians with PTSD. Multiple regression analyses demonstrated a significant association between the hyperarousal subscale of the PTSD Checklist for DSM-5 (PCL-5) and the Fear of Sleep Inventory total score (FoSI). FoSI was also associated with objective indices of hyperarousal during sleep, including mean pulse rate and number of awakenings.2 The authors concluded that fear of sleep may be a symptom of heightened sympathetic activation and drive for vigilance common in PTSD. These results nicely complement the findings of our paper demonstrating an association between FoSI and hypervigilance intensity, FoSI and nightmare frequency, and FoSI and disruptive behaviors during sleep (eg, nocturnal panic attacks) in individuals with PTSD and insomnia.3

Although not presented in their letter, Gupta and Sheridan reported in their cited abstract that FoSI was associated with respiratory disturbance and oxygen desaturation.2 These results highlight the possible link between FoSI and sleep-disordered breathing, which may be related to apnea-related sympathetic activation, but also potentially an anxiogenic response to hypoxia.

In their cited abstract, Gupta and Sheridan also found that FoSI was associated with longer sleep onset latency and poorer sleep efficiency.2 These results are consistent with previous studies, which have demonstrated an association between fear of sleep and insomnia symptoms and have led authors to postulate that fear of sleep may be involved in the pathogenesis of insomnia in PTSD. Interestingly, our team failed to find an association between FoSI and insomnia symptoms.3 One possible explanation for these mixed findings is based on a hypothesis proposed by Zayfert and DeViva.4 PTSD symptomatology (eg, hypervigilance) may be driving fear of sleep, which in turn leads to insomnia-related sleep disruptions (eg, longer sleep onset). Over time, insomnia develops into a learned behavior pattern that persists even after precipitating factors are removed (eg, fear of sleep). This may explain why we did not find an association between insomnia symptoms and FoSI in our sample. By the time study participants received treatment, their insomnia symptoms were no longer driven by PTSD-related precipitating factors. This theory also explains why cognitive behavioral therapy for insomnia (CBT-I), even without a focus on nightmares or specific trauma-related content, is effective in individuals with PTSD.5 Interestingly, despite not being a treatment target, we found a reduction in fear of sleep, which was related to a decrease in hypervigilance, following CBT-I. Future studies should consider examining whether a decrease in sympathetic activation following CBT-I is a potential mechanism for this change.

We appreciate Dr. Gupta and Ms. Sheridan's letter to the editor. Their work is an important contribution to the literature examining the complexities of sleep disturbance in PTSD.


All authors have seen and approved the manuscript. The authors report no conflicts of interest.


Kanady JC, Maguen S, Neylan TC. Further exploring the associations between sympathetic activation, fear of sleep, and insomnia symptoms in posttraumatic stress disorder. J Clin Sleep Med. 2018;14(12):2095–2096.



Gupta MA, Sheridan AD. Fear of sleep may be a core symptom of sympathetic activation and the drive for vigilance in posttraumatic stress disorder. J Clin Sleep Med. 2018;14(12):2093


Gupta MA, Sheridan AD. Fear of sleep (FS) in posttraumatic stress disorder (PTSD) patients correlates directly with indices of hyperarousal during wakefulness and sleep. Sleep. 2018;41 Suppl 1:A348


Kanady JC, Talbot LS, Maguen S, et al. Cognitive behavioral therapy for insomnia reduces fear of sleep in individuals with posttraumatic stress disorder. J Clin Sleep Med. 2018;14(7):1193–1203. [PubMed Central][PubMed]


Zayfert C, DeViva JC. Residual insomnia following cognitive behavioral therapy for PTSD. J Trauma Stress. 2004;17(1):69–73. [PubMed]


Talbot LS, Maguen S, Metzler TJ, et al. Cognitive behavioral therapy for insomnia in posttraumatic stress disorder: a randomized controlled trial. Sleep. 2014;37(2):327–341. [PubMed Central][PubMed]