16A major problem in psychology and physiology experiments is drowsiness: around a third of 17 participants show decreased wakefulness despite being instructed to stay alert. In some non-18 visual experiments participants keep their eyes closed throughout the task, thus promoting the 19 occurrence of such periods of varying alertness. These wakefulness changes contribute to 20 systematic noise in data and measures of interest. To account for this omnipresent problem in 21 data acquisition we defined criteria and code to allow researchers to detect and control for 22 varying alertness in electroencephalography (EEG) experiments. We first revise a visual-scoring 23 method developed for detection and characterization of the sleep-onset process, and adapt the 24 same for detection of alertness levels. Furthermore, we show the major issues preventing the 25 practical use of this method, and overcome these issues by developing an automated method 26 based on frequency and sleep graphoelements, which is capable of detecting micro variations in 27 alertness. The validity of the automated method was verified by training and testing the algorithm 28 using a dataset where participants are known to fall asleep. In addition, we tested generalizability 29 by independent validation on another dataset. The methods developed constitute a unique tool 30 to assess micro variations in levels of alertness and control trial-by-trial retrospectively or 31 prospectively in every experiment performed with EEG in cognitive neuroscience. 32

Despite a surge of studies on the effects of COVID-19 on our well-being, we know little about how the pandemic is reflected in people's spontaneous thoughts and experiences, such as mind-wandering (or daydreaming) during wakefulness and dreaming during sleep. We investigated whether and how COVID-19-related general concern, anxiety, and daily worry are associated with the daily fluctuation of the affective quality of mind-wandering and dreaming, and to what extent these associations can be explained by poor sleep quality. We used ecological momentary assessment by asking participants to rate the affect they experienced during mind-wandering and dreaming in daily logs over a 2-week period. Our preregistered analyses based on 1,755 dream logs from 172 individuals and 1,496 mind-wandering logs from 152 individuals showed that, on days when people reported higher levels of negative affect and lower levels of positive affect during mind-wandering, they experienced more worry. Only daily sleep quality was associated with affect experienced during dreaming at the within-person level: on nights with poorer sleep quality people reported experiencing more negative and less positive affect in dreams and were more likely to experience nightmares. However, at the between-person level, individuals who experienced more daily COVID-19 worry during the study period also reported experiencing more negative affect during mind-wandering and during dreaming. As such, the continuity between daily and nightly experiences seems to rely more on stable trait-like individual differences in affective processing.

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