Introduction
Objective measures of sleep quality do not fully explain variance in morning reports of feeling rested. What predicts this consequential difference? Sleep duration and quality, as well as chronotype, were documented to impact how energetic people feel in the morning. Very little is known about the impact of positive affect at night on morning energy levels.
Methods
In a sample of 1302 participants (72.6% female, age range 13–65, mean 30.8 years), we used ecological momentary assessment (EMA) to examine the relation between self-reports of nighttime happiness and next-morning energy levels (rated from 0–100). We included only participants who (a) rated their happiness between 8PM-2AM, (b) reported their energy level and sleep duration between 5AM-11AM on the following day, and (c) rated their chronotype (0 = extreme morning type, 100 = extreme evening type).
Results
Hierarchical linear models suggest that greater nighttime happiness predicts higher ratings of energy the following morning (b = 0.46, SE = 0.02, p < 0.0001), regardless of sleep duration and chronotype. Additionally adjusting for average morning happiness level, which is strongly correlated with morning energy (r = 0.49), evening happiness still predicted next-morning energy (b = 0.19, SE = 0.04, p < 0.0001). The association remained significant but was slightly reduced when limited to weekend responses (n = 364, b = 0.18, SE = 0.04, p < 0.0001). In this sample, chronotype did not predict morning energy rating after adjusting for happiness and sleep duration.
Conclusion
Greater positive pre-sleep affect was correlated with subjective experiences of greater next-morning energy level, regardless of self-reported sleep duration, average morning happiness, and chronotype. Although the EMA method allows for data collection in a large sample, limitations include variability in the timing of assessments relative to sleep onset and offset and absence of information about sleep disturbances. Our novel findings, if replicated, imply that interventions to address pre-sleep affective states may lead to improved daytime energy levels.