Temporal Associations Between Physiological Sleep and Next‐Day Pain Intensity in Individuals With Activity‐Limiting Chronic Pain: A Multiple Night At‐Home Ear‐ EEG Sleep‐Monitoring Study

Chronic pain and sleep disturbances frequently co-occur. However, most prior research relies on self-report or actigraphy, which reflect behavioural aspects of sleep but provide only limited insight into the underlying sleep physiology. In this pre-registered prospective observational study (NCT06368531), we investigated within-person night-to-night variability in physiological sleep metrics and explored temporal associations between sleep metrics and next-day pain. Individuals with bothersome (n = 4) or high-impact (n = 15) chronic pain completed between 11 and 33 nights of at-home sleep monitoring using an ear-EEG device and rated morning pain intensity daily on a 0-10 numerical rating scale. This design enables assessment of real-world physiological sleep patterns alongside natural fluctuations in pain, offering a high-resolution view of sleep-pain dynamics beyond traditional diary or actigraphy-based methods. Substantial between-night variability was observed across multiple sleep metrics, such as sleep efficiency and sleep stage transitions (ICC values < 0.5), indicating that less than half of the total variance was attributable to differences between subjects, underscoring the importance of longitudinal within-person monitoring. Mixed-effects model analyses revealed that lower next-day pain intensity was associated with greater duration (β = -0.01, p = 0.005), higher percentage (β = -0.07, p = 0.001) and increased stability (β = -0.01, p = 0.013) of N3 sleep. In contrast, higher next-day pain was associated with increased N3 fragmentation (β = 0.01, p = 0.014) and a higher proportion of N1 sleep (β = 0.014, p = 0.007). Together, these findings provide objective physiological support for previously reported associations between sleep and pain, highlighting the value of longitudinal ear-EEG monitoring for capturing nightly sleep-pain dynamics. Trial Registration: ClinicalTrials.gov identifier: NCT06368531.