Subjective sleep quality, but not objective sleep measures, mediates the relationship between pre-sleep worrying and affective wellbeing.

Pre-sleep worrying is associated with sleep disturbance, which in turn is associated with impaired affective wellbeing. However, studies examining the fine-grained temporal order of these variables are still lacking. In particular, within-person mediation of the association between pre-sleep worrying and the following day's affective wellbeing by subjective and objective indicators of sleep has not been tested yet. This study investigates the extent to which pre-sleep worrying predicts positive/negative affect the following day, and whether subjective/objective sleep disturbances are possible mediators for this relationship. Data from two experience sampling studies were pooled for the analyses, resulting in a total sample of 220 participants aged between 18 and 30 years (M = 23.2 years, SD = 2.8). The hypotheses were tested at both the between- and within-subject level using causal mediation analysis. The within-subject analyses revealed partial mediation of the relationship between pre-sleep worrying and positive as well as negative affect the next day by subjective sleep quality. By contrast, sleep as measured by actigraphy appears not to be relevant for the link between pre-sleep worrying and affective wellbeing the following day. Baseline levels of depressive symptoms and sleep disturbances did not moderate the associations between pre-sleep worrying, sleep indices and affective states the following day. Improving perceived sleep quality by addressing pre-sleep worrying could be a potential avenue to enhance affective wellbeing and promote better mental health in young adults.