Can Netflix keep you awake at night?

Binge-watching suspenseful TV series with cliffhangers before sleep has only minor effects on sleep. This has been shown by researchers from the University of Fribourg. The study shows what happens in your brain when we sleep after a binge-watching session. 

Does binge-watching suspenseful series before sleep have a real impact on our sleep? Professors Björn Rasch and Andreas Fahr from the University of Fribourg tried to answer that question in an SNF-funded project titled «Excessive Media Use in Times of Netflix». They investigated the new phenomenon of binge watching of series, the underlying motives and experiences and its effects on sleep. In a study newly published in the journal Sleep Medicine, they focused particularly on the effect of this activity on pre-sleep arousal and subsequent sleep.

Cliffhangers increase pre-sleep arousal
Feeling aroused is associated with more sleep difficulties, a longer to fall asleep or a more fragmented sleep. Indeed, the symptoms of arousal, for example a higher heart rate or ruminations, are complete opposite to the physical and mental states that promote a good quality sleep. The newly published study shows that binge-watching suspenseful series increase the perceived feeling of stress. However, the physiological aspects of arousal such as higher heart rate or higher level of cortisol are only observed when the series end with a cliffhanger, explains PhD student Sandrine Baselgia from the Department of Psychology.

Only minor effects on sleep
50 healthy young sleepers took part in the Unifr study. They spent two nights in a sleep laboratory. On one night, they binge-watched 3-4 episodes of a suspenseful TV series before going to bed. On the other night, they binge-watched a neutral documentary series for the same amount of time before going to bed. For one group of participants, the suspenseful series ended with a cliffhanger right before sleep while for the other group, the ending of the suspenseful series was manipulated to end in a calm situation. To objectively measure their sleep, the electrical activity of their brain was measured with an electroencephalogram (EEG). The focus was on the time needed to fall asleep and sleep quality. The latter was measured both subjectively – as reported by the participants on the next morning – and objectively – with the amount of deep sleep and the ratio between slow and fast EEG oscillations (i.e. a higher ratio indicating a more restorative sleep).

In spite of the clearly increased pre-sleep arousal, Sandrine Baselgia and Björn Rasch were able to show that the effects of a suspenseful series on sleep quality were not majorly different from those of neutral documentary. The differences in the subjective rating of sleep quality were only minor. To the research’s surprise, the sleep onset latency even was significantly reduced after the suspenseful TV series. However, it was also observed that the test subjects spend less time in deep sleep when the series end with a cliffhanger compared to no cliffhanger. This effect was especially visible in the first two sleep cycles (approximately three hours). The same pattern of result is found in the EEG oscillations: the ratio between slow and fast EEG waves was lower when binge-watching a suspenseful series ending with a cliffhanger as compared to no cliffhanger and the neutral documentary which indicates a less restorative sleep.

Stop watching before the cliffhanger
«We assume that the suspense associated with the open endings after watching TV series with cliffhangers is spontaneously reactivated during sleep. This reactivation could trigger associated bodily functions and wake-promoting brain regions, thereby reducing the depth of sleep», says Björn Rasch. Most importantly, the study results show that TV series ending with cliffhangers can increase arousal and reduce the recovery function of sleep. Therefore, it is still recommended to reduce the use of cliffhangers in TV series, or at least stop the episode before, if we want to enjoy a healthy sleep.

Baselgia S., Combertaldi S.L., Fahr A., Wirz D.S., Ort A. & Rasch B.: Pre-sleep arousal induced by suspenseful series and cliffhangers have only minor effects on sleep: A sleep laboratory studySleep Medicine, 102. 2023