Frequent dreams and nightmares became more common worldwide during the COVID-19 pandemic, according to a new international study published in the Journal of Sleep Research.
While dreaming has long fascinated scientists, much of what is known about how often people recall dreams or experience nightmares has come from studies conducted in individual countries—mostly in Europe. These studies often used different definitions and tools, making it difficult to compare findings across populations.
A new study, led by an international team of researchers from institutions across Europe, Asia, the Americas, and Australia, aimed to provide a clearer picture of how frequently people recall dreams or experience nightmares—and how these patterns vary by age, gender, and sleep duration.
Led by Courtney J. Bolstad, the research team was particularly interested in how the global disruption caused by the COVID-19 pandemic may have influenced sleep and dream experiences.
To investigate this, the researchers surveyed 15,854 adults aged 18 to 99 (69.9% women) using a standardized online questionnaire as part of the International COVID-19 Sleep Study. Data were collected between May and November 2021 across 16 countries. Importantly, the same survey instrument was used in every country to ensure consistency.
Participants were asked to report how often they recalled dreams or had nightmares in two time periods: retrospectively for 2019 (pre-pandemic) and currently in 2021 (during the pandemic). They also reported their average nightly sleep duration for both years.
In 2021, 54% of participants reported recalling dreams at least once a week, compared to 51.1% in 2019. Nightmares showed a sharper increase: 11% of participants reported experiencing nightmares at least weekly in 2021, compared to just 6.9% in 2019.
There were notable differences between countries. In 2021, Brazil had the highest rates of frequent dream recall and nightmares, while Germany reported some of the lowest rates of both. In 2019, the United States had the highest rates for both frequent dreams and nightmares. Israel consistently reported the lowest rates of nightmares across both years.
Demographic factors also played a significant role. Younger adults were more likely than older adults to frequently recall dreams and experience nightmares. Women reported both experiences more often than men in 2021, though in 2019, men reported slightly more nightmares.
Sleep duration was another key factor. People who slept longer were more likely to recall dreams frequently—a relationship that followed a linear pattern. Nightmares, however, followed a U-shaped pattern: they were more common among both short sleepers (less than 6 hours) and long sleepers (more than 9 hours), and least common among those who slept 6 to 9 hours per night.
“We suspect insomnia may explain the relation between nightmares and short sleep duration, while increased REM sleep may explain the association between long sleep duration and dream recall and nightmares,” the authors noted.
However, the study also has some caveats. Because people were asked in 2021 to remember their 2019 sleep patterns, their memories might not be perfectly accurate. Recruitment methods varied slightly by country, and the research didn’t explore other factors such as stress, trauma, or COVID-19 infection – which could all influence dreaming.
The study, “Prevalence Rates of Frequent Dream Recall and Nightmares by Age, Gender and Sleep Duration in 16 Countries,” was authored by Courtney J. Bolstad, Bjørn Bjorvatn, Ngan Yin Chan, Frances Chung, Yves Dauvilliers, Luigi De Gennaro, Colin A. Espie, Brigitte Holzinger, Yuichi Inoue, Maria Korman, Adrijana Koscec Bjelajac, Anne-Marie Landtblom, Tainá Macêdo, Kentaro Matsui, Ilona Merikanto, Charles M. Morin, Sérgio Mota-Rolim, Thomas Penzel, Giuseppe Plazzi, Cátia Reis, Serena Scarpelli, Yun Kwok Wing, and Michael R. Nadorff.