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The Larry Davids, Monica Gellers, Niles Cranes, Ally McBeals and Mitchell Pritchetts of the world might be at a disadvantage when it comes to getting rest. If it's not obvious from this list of (mostly) fictional over-thinkers and nitpickers, neuroticism is the personality trait most directly and consistently linked to insomnia and other sleep problems. 

It might not be surprising that being neurotic and sleeping poorly go together like a fever and chills. Neurotic people are, after all, prone to anxiety, depression, loneliness and other issues that interfere with easy rest. But the strength of the neuroticism-sleep link, across diverse groups of people, is noteworthy. Now, researchers are trying to figure out which aspects of neuroticism are responsible for poor sleep and what, precisely, goes wrong at night for those of us who have no chill.

In the world of behavior science, personality traits are thought of as "the relatively enduring patterns of thoughts, feelings and behaviors that make people uniquely themselves." And, dating back to the early 20th century, psychologists have proposed methods for summarizing someone's personality. In the 1930s, Gordon Allport, the "father of personality psychology," identified 4,500 traits that play a role in making us who we are. But, today, most researchers rely on the much simpler "Big Five" framework, which breaks down personality into five essential traits: conscientiousness, agreeableness, openness to experience, extraversion and, of course, neuroticism. 

This means that your personality is linked to your own beliefs about how you sleep rather than results from an objective sleep test.

Using the Big Five, researchers have found that personality traits are predictive of self-reported sleep quality. This means that your personality is linked to your own beliefs about how you sleep rather than the results of an objective sleep test. And, across a number of studies — involving both college kids and less-young adults, from different countries — researchers have identified high neuroticism as the strongest predictor of poor sleep. 

In one recent study, for example, sleep-and-cognition researchers from The Netherlands examined personality traits and insomnia. There’s more to the can’t-sleep disease than not being able to nod off; other features include difficulty staying asleep, unrefreshing sleep and poor daytime functioning. Here, researchers examined how specific insomnia symptoms were related to the Big Five traits. 

To do this, they analyzed surveys completed by 2,089 volunteers, aged 18-84, between 2012 and 2016. Their survey data came from the Netherlands Sleep Registry, a database that "assesses traits across the general population to facilitate research on traits that distinguish insomniacs and normal sleepers.” 

Of the Big Five traits, neuroticism had the strongest link to insomnia — especially to two symptoms: difficulty falling asleep and poor daytime functioning. Conscientiousness also predicted insomnia, but to a lesser degree and in a different way. Conscientious people said it was tough to stay asleep, but they weren't likely to say they had trouble getting through the day as a result. 

In another study, published earlier this year, a team of American and Italian researchers tried to figure out which aspects of neuroticism are responsible for its connection to poor sleep. For the study, 498 Italian adults filled out surveys on sleep quality and personality traits, as well as on three other individual differences: 1) positive and negtive affect, which (respectively) describe a person's tendency to experience positive moods and negative moods; 2) dysfunctional emotional regulation strategies, which are unhealthy styles of dealing with stress; and 3) hyper-arousal.

Personality traits will also shape how people cope with stress and likely relate to hyperarousal.

These individual differences have been associated with poor sleep in earlier work. And, like the Big Five, they appear to remain relatively stable across time, explained Nicola Cellini, a psychologist at UC Riverside who co-authored the study. "In a sense, they are components of personality traits," said Cellini. "And personality traits will also shape how people cope with stress and likely relate to hyperarousal."

As predicted, neuroticism was the best predictor of sleep quality. But, unlike in the study from The Netherlands, Cellini and colleagues found a link between poor sleep and low (rather than high) conscientiousness. And, when researchers added the other, non-Big Five individual differences into the mix, they found that low positive affect, high negative affect and hyperarousal predicted poor sleep quality, both on their own and when combined with personality traits. Based on these findings, researchers surmised that neurotic people suck at sleeping because pre-bed ruminating leaves them aroused and extra-sensitive to minor sleep disturbances, rather than because of the way they manage stress. 

The results overall suggested to researchers that individual differences help explain why neurotic people have consistently been the biggest sleep-kvetchers in studies on The US, Turkey, South Korea and Finland. "The distribution of the personality traits changes across countries. Similarly, sleep quality is affected by the country and culture you live in," said Cellini. "Despite this, individual differences predict sleep quality in similar ways."

You might be genetically predisposed to be hyperactive, and this biologically-driven hyperactivity can also be the cause your personality and sleep quality.

In fact, this study supports the idea that sleep quality and personality traits are shaped by the same genes for individual differences. "For example," Cellini said, "you might be genetically predisposed to be hyperactive, and this biologically-driven hyperactivity can also be the cause your personality (e.g., highly neuroticism) and sleep quality (e.g., you have difficulties relaxing, falling asleep and maintaining a continuous unfragmented sleep during the night."

It might also be the case, said Cellini, that people with certain Big Five traits or sleep habits "end up in the same kinds of situations repeatedly (e.g., staying out late at a bar), which might reinforce their personality traits and sleep quality across time, leading them to become more strongly correlated."

At this point, the dynamic between neuroticism (or personality traits in general), poor sleep and these ever-illusive individual differences offers a lot of questions to mull over. And who's better at mulling over unresolved situations than neurotic people?