Sleep extension: an explanation for increased pandemic dream recall?

Dear Editor, The Coronavirus Disease 2019 (COVID-19) pandemic has dramatically impacted the lifestyle of individuals across the globe. In many countries, nationally instituted shelter-in-place orders and closures of non-essential businesses have left many without employment and have forced others to work from home. These policy shifts have changed or removed the socially- and occupationally imposed demands that typically influence sleep schedules. Lifestyle and schedule changes that have stemmed from the COVID-19 pandemic have not gone unnoticed to those in the sleep research and sleep medicine communities. Several recently published and ongoing studies have aimed to track sleep and sleep-related behaviors during these unprecedented times. Initial reports suggest that sleep duration and quality changed during the early phases of the pandemic. For instance, multiple studies found increased sleep duration [1, 2] and time in bed [2, 3] in populations under varying degrees of lockdown (e.g. in the United States and in four European countries). However, unexpectedly, the same studies found a decrease in self-reported sleep quality [1, 3]. To explain these paradoxical findings, the authors proposed that increased stress from life changes (e.g. loss of employment, financial hardship, or new childcare demands) or increased psychological health issues (e.g. anxiety, loneliness) may have negatively impacted sleep quality despite increased total sleep time. In parallel, anecdotal evidence has surfaced that individuals are remembering more dreams and that dream content has become more vivid during the pandemic. Such reports have been covered by a number of major news outlets, including the New York Times, Time magazine, Smithsonian magazine, and National Geographic magazine. Many have turned to the dream simulation theory, which posits dreams provide a chance to “work out” future or current threatening or social scenarios [4], to explain why dream frequency and content are changing. However, we are not aware of any empirical work that has explored or confirmed this hypothesis. We posit that the three phenomena described above—longer sleep, more fragmented sleep, and frequent/vivid dream recall—are not coincidental. Instead, these sleep behaviors might all be caused by naturalistic “sleep extension,” which is defined as the act of extending one’s sleep duration beyond habitual levels [5]. Sleep extension has been used as a research tool for decades, and, more recently, has been implemented in both controlled and applied research settings as a means to “bank” sleep [6]. Studies on sleep extension have provided unique insight into the nature of reducing “sleep debt” and the limits of the sleep homeostat. That is, they hint at what might happen when an individual has unrestricted time for sleep over an extended period of time—something akin to what might be the case for some individuals during the COVID-19 pandemic. Experimental evidence has shown that although sleep duration tends to increase during the early stages of sleep extension (e.g. the first 7–10 days [5]), once sleep debt has been “satiated,” sleep duration tends to regress toward habitual levels. Importantly, if a continued attempt to extend sleep is made following sleep debt satiation, sleep continuity decreases and sleep becomes more fragmented [7, 8]. Dream recall is increased by more frequent awakenings, as demonstrated in a recent study in which self-reported high-frequency dreamers had more nighttime awakenings than low-frequency dreamers [9]. These findings are in support of the arousal-retrieval model of dream recall, which suggests individuals with higher dream recall may not necessarily dream more frequently. Rather, frequent awakenings simply provide more opportunities for memory encoding, rehearsal, and consolidation of dream content. Although no study has directly assessed the link between sleep extension, sleep fragmentation, and dream recall, at least one study has reported an increase in dream recall following experimental sleep extension, though the content of the dreams was not reported, as this was not the main objective of the study [10]. In conclusion, we hypothesize that increased dream recall during the COVID-19 pandemic may be attributable to increased sleep fragmentation caused by naturalistic sleep extension. However, we do not present this as a “unifying hypothesis” to explain all sleep changes and issues during the pandemic. Certainly, stress, anxiety, and social separation may play a role in impacting sleep. Further, we do not have hypotheses on whether sleep extension and consequent fragmentation influence the content of the dreams. The hypothesis proposed here is, therefore, not in opposition to those on changes in dream content or vividness (e.g. the simulation theory [4]). We look forward to future work on these topics and to gaining a greater understanding of how sleep and circadian processes are being impacted during this critical and unprecedented time. Understanding the relationship between pandemic-related schedule changes, psychosocial changes, and sleep changes will provide insight to guide sleep-related recommendations during future comparable scenarios, should any arise. We would like to thank the brave first responders and military service members that have compromised their health and sleep during the COVID-19 pandemic. In particular, R.B. and T.J.C. would like to acknowledge our partners, Dr. Dorothy Liu, MD and Kate Cunningham, RN, respectively, who continue to amaze us with their commitment to the health and wellbeing of their patients. Material has been reviewed by the Walter Reed Army Institute of Research. There is no objection to its presentation and/or publication. The opinions or assertions contained herein are the private views of the authors and are not to be construed as official, or as reflecting true views of the Department of the Army or the Department of Defense. The investigators have adhered to the policies for the protection of human subjects as prescribed in AR 70–25. None declared. Conflict of interest statement. None declared.