National trends in prevalence of sadness, counseling for sadness, and sleep time among Koreans amid pandemic, 2009-2021: a nationwide representative study of over 2.8 million individuals

COVID-19 broadly worsened the health of infected patients, and even those who were not infected experienced various quarantine policies and concern of being infected which subsequently impacted mental health and wellbeing in various detrimental ways (Cha et al., 2023; Partinen, 2021; Vos et al., 2020). There are numerous reports investigating the mental health of individuals during the pandemic, including studies on sadness and sleep patterns (Partinen, 2021; Vos et al., 2020). However, there is a paucity of large-scale studies that track the prevalence of sadness during the pandemic. To date, most studies on sadness and sleep of individuals amid the COVID-19 pandemic were based on subpopulations, such as healthcare workers and college students (Jahrami et al., 2021; Pappa et al., 2020). Hence, we aimed to determine whether levels of sadness had changed from before to during the pandemic, as well as sleep time among adults and compare the changes in trend with those of 13 years preceding the pandemic. The results will shed light on those trends on a large-scale.