Exploring the bidirectional within-subject relationship between sleep and affective wellbeing: Insights from an intensive longitudinal study

This study aimed to investigate the bidirectional relationships between affective wellbeing and sleep, and to explore the moderating effects of depressive and insomnia symptoms. Data from two studies, involving 178 participants in total aged 18-29 years, were analyzed. Over 14 days, participants completed daily surveys assessing affective wellbeing and wore ECG chest belts for heart rate variability monitoring to derive objective sleep indices. Multilevel models were used to examine within-subject associations between affective states and subsequent sleep, and vice versa, while considering depressive and insomnia symptoms as moderators. Higher positive affect than usual in the evening was associated with shorter total sleep time, shorter rapid eye movement sleep, and lower number of awakenings and stage shifts than usual in the following night. Regarding sleep predicting morning's affective wellbeing, longer slow-wave sleep was linked to higher positive affect than usual, while longer rapid eye movement sleep and higher sleep efficiency than usual predicted lower negative affect than usual. Also, higher subjective sleep quality than usual was associated with higher positive and lower negative affect than usual the next morning. No evidence for moderation effects of insomnia and depressive symptoms for the bidirectional within-subject associations between sleep and affect was found. The findings underscore the complex interplay between sleep and affective wellbeing, particularly highlighting that the subjective perception of one's sleep appears to be relevant for the next morning's affective states.