Korean Survey Analysis Shows Morning Sleep Inertia Associated With Sleep Patterns and Anxiety

A recently published analysis from the population-based, cross-sectional Korean Sleep Headache Study showed that sleep inertia, the period of grogginess experienced upon waking, was associated with sleep duration, chronotype, sleep-related symptoms, and anxiety among adults in Korea.^1,2 The findings, published in PLoS One, highlight the need for targeted interventions to reduce the adverse impact of sleep inertia on daily functioning in adults.

Among 2355 participants (men, 49.2%, age, 19-92 years) included in the analysis, researchers reported that morning sleep inertia was significantly associated with several sleep characteristics (P <.001 for all), despite the small effect sizes. Authors noted that individuals with a shorter sleep duration (18.0 [SD, 16.5]) had longer sleep inertia compared with those with intermediate (15.8 [SD, 12.9] minutes) or longer sleep duration (14.0 [SD, 9.9] minutes).

Additional findings revealed that individuals with an evening chronotype demonstrated longer mean sleep inertia compared with those with morning or intermediate chronotypes (17.7 [SD, 13.6] vs 14.3 [SD, 12.1] and 15.5 [SD 12.9], respectively). Longer sleep inertia was also reported among participants with insomnia (20.7 [SD, 16.7] vs 14.8 [SD, 11.8]), excessive daytime sleepiness (EDS, 18.7 [17.9] vs 15.2 [SD, 11.8]), anxiety (29.9 [SD, 21.7] vs 15.6 [SD, 12.7]), and depression (19.8 [SD, 15.3] vs 15.4 [SD, 12.6]) compared with those without these conditions (P <.001 for all comparisons).

“One of the most clinically important findings of our study is that anxiety showed the strongest association with prolonged sleep inertia, even after accounting for sleep duration, chronotype, and other sleep-related factors,” senior author Chang-Ho Yun, MD, PhD, professor in the Department of Neurology at Seoul National University College of Medicine, told NeurologyLive^®. “This suggests that sleep inertia should not be viewed solely as a consequence of insufficient or poor-quality sleep, but rather as a multidimensional phenomenon reflecting both sleep physiology and emotional regulation. Clinically, this means that patients presenting with excessive morning grogginess may benefit from assessment of anxiety symptoms, as these may be a key contributing factor.”

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In this study, researchers investigated characteristics and associations with sociodemographic factors, sleep patterns, and comorbidities in an adult population using data from the 2018 Korean Sleep Headache Study. Morning sleep inertia was measured by self-reported duration in minutes required to resolve grogginess after waking. In addition, authors assessed chronotype, sleep duration, sleep quality, lifestyle factors, and mood variables. The mean duration of morning sleep inertia in the overall population was 15.8 minutes (SD, 12.9), with women reporting significantly longer sleep inertia compared with men (16.3 [SD, 13.2] vs 15.2 [SD, 12.7], P = .03, respectively).

“In clinical practice, differentiation can be approached by evaluating three domains: sleep duration, circadian preference, and associated daytime symptoms. Sleep-related drivers are more likely when sleep inertia co-occurs with short sleep duration, evening chronotype, or insomnia symptoms,” Yun added. “In contrast, when sleep timing and duration are relatively adequate but sleep inertia remains pronounced—particularly with prominent anticipatory discomfort or cognitive fog upon awakening—psychiatric factors such as anxiety should be considered. Our findings also suggest that these relationships may vary by sex and chronotype, highlighting the importance of individualized assessment.”

In multiple linear regression analyses adjusted for age and sex, log-transformed sleep inertia was evaluated as a continuous outcome. Shorter sleep duration, morning chronotype, and habitual snoring were inversely associated with sleep inertia, whereas evening chronotype, insomnia, EDS, and anxiety were positively associated with longer sleep inertia durations. In sex-stratified models, sleep duration, chronotype, and insomnia remained significantly associated with sleep inertia in both men and women. Anxiety was significantly associated with sleep inertia in men only, whereas habitual snoring and EDS were significant in women only.

Subgroup analyses by chronotype demonstrated additional variation. Insomnia was consistently associated with longer sleep inertia across all chronotype groups. Sleep duration showed an inverse association with sleep inertia among individuals with intermediate and evening chronotypes, whereas habitual snoring was inversely associated in those with an evening chronotype. EDS and anxiety were positively associated with sleep inertia in evening and morning chronotypes, respectively. Anxiety demonstrated the strongest overall association, particularly among males and individuals with a morning chronotype.

“Our results suggest that interventions should be tailored to the dominant underlying mechanism. For individuals with insufficient sleep or circadian misalignment, optimizing sleep duration and stabilizing sleep–wake schedules may be key,” Yun told NeurologyLive. “For those with insomnia symptoms, evidence-based behavioral interventions such as cognitive behavioral therapy for insomnia may be beneficial. Importantly, given the strong association with anxiety, incorporating strategies that target emotional regulation may be particularly effective in selected patients. In many cases, a combined approach addressing both sleep regulation and psychological factors is likely to yield the greatest benefit.”

“Overall, our study highlights sleep inertia as a clinically relevant and under-recognized condition that reflects the interaction between sleep, circadian, and emotional processes, and may serve as a useful target for personalized interventions,” Yun added.

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REFERENCES
1. Kim JR, Park HJ, Paik SM, et al. Morning sleep inertia and its associated factors: Findings from a nationwide study. PLoS One. 2026;21(1):e0337992. Published 2026 Jan 2. doi:10.1371/journal.pone.0337992
2. Hilditch CJ, McHill AW. Sleep inertia: current insights. Nat Sci Sleep. 2019;11:155-165. Published 2019 Aug 22. doi:10.2147/NSS.S188911