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Sleep disorders bring out the bad sides

28.6.2025

Translation: machine translated

People who have not slept well are more likely to behave narcissistically, manipulatively and unscrupulously at work the next day.

Is one of your colleagues only ever thinking about themselves? This could be because they suffer from sleep problems, as a field study among employees in Belgium and Argentina suggests. Those who did not get a good night's rest last night are more likely to show their bad side the next day, the researchers conclude in the specialist journal «Journal of Organizational Behavior».

The team led by psychologist Evy Kuijpers from the Free University of Brussels wanted to find out under what circumstances any negative traits come to light in the workplace. The group therefore asked more than 100 employees in Belgium and Argentina to provide information about their everyday working life via an app for ten days: In the morning, the participants noted how well and how long they had slept; in the afternoon, they reported on how they dealt with stress and their behaviour at work. Did they display characteristics of narcissism, Machiavellianism or psychopathy, the so-called dark triad of personality? For example, had they lied to someone or taken advantage of them?

The result: those who had slept briefly or poorly were less able to deal with unpleasant situations and were more likely to show signs of narcissism, Machiavellianism and psychopathy, such as an increased need for admiration, manipulative behaviour and lack of conscience. Even small fluctuations in sleep duration and sleep quality were reflected in their behaviour the next day. The reverse was not the case: if someone reported characteristics of the dark triad during the day, they did not sleep worse as a result. In the case of manipulative behaviour, the subsequent night's sleep was even better.

The correlation could not simply be explained by the respondents' general tendency towards narcissism, Machiavellianism and psychopathy. The researchers conclude that stable personality traits alone are not enough to explain antisocial behaviour. It is only in the interaction with other conditions such as sleep problems and stress that personality emerges.

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