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Worried you might say something you regret when talking in your sleep? Your concerns may be justified: According to a recent study from France, your midnight mumblings may be more negative and insulting than what you say while awake.

In the study, researchers found that sleep talkers said the word “no” four times as often in their sleep as when awake. And the f-word popped up during sleep talking more than 800 times more frequently than while awake.

To study sleep talking, the researchers recorded nearly 900 nighttime utterances from about 230 adults during one or two consecutive nights in a sleep lab. Because sleep talking is a relatively rare event, the majority of people in the study had certain types of sleep disorders, or parasomnias, which are unusual behaviors that happen during sleep, the researchers noted.

Once recorded, the nocturnal episodes were analyzed for such factors as wordiness, silences, tone, politeness and abusive language. These results were compared to see how sleep speech matched up to everyday spoken French in form and content.

The researchers found that the majority (59 percent) of the nighttime utterances were unintelligible or nonverbal, including mumbling, whispering and laughing.

But among the utterances that were intelligible, a surprising amount of what was said was offensive or aggressive: 24 percent contained negative content, 22 percent had “nasty” language and almost 10 percent contained the word “no” in some form. (By comparison, the word “no” accounted for 2.5 percent of awake language.)

The f-word also made a frequent appearance and was one of the most common words spoken during sleep talking: It showed up 2.5 percent of the time, compared with just 0.003 percent of spoken words while awake. In total, 10 percent of all clauses spoken during sleep contained profanity.

Why so negative? The findings may reflect what’s called the “threat simulation theory,” which is one explanation for the function of dreams, according to the study. The theory posits that dreams are simulations that help train people for threats that could happen while awake, providing an evolutionary purpose for dreaming.

Although the study participants were French, the findings don’t necessarily mean that French people are ruder than other nationalities, said lead study author Isabelle Arnulf, a neurologist in Paris. In fact, the study mirrors anecdotal findings of sleep talk content from abroad, Arnulf said.

And although the content spoken during sleep may have been more offensive and nasty, the speech was otherwise similar to that used when awake, Arnulf said. Sleep talking tended to remain grammatically correct and followed patterns of everyday speech regarding pauses and the number of words used in a given statement.

Carl Bazil, director of the Division of Sleep and Epilepsy at Columbia University, who was not involved in the study, said that the findings show that sleep speech is much more “complex than expected” and supports the idea that there is “higher brain function” during all stages of sleep.

Indeed, the fact that the phrases spoken during sleep were largely grammatically correct suggests that the same neural system is functioning as when people are awake, according to the study. At the same time, the large amount of mumbling shows that there is still some motor inhibition at play; in other words, the brain is still blocking muscle movement.

Ultimately, the sleep speech in the study suggests a complex level of brain functioning that could help give scientists more insight into the purpose and process of dreams, even if, at the same time, it shows a less-than-flattering side of ourselves, the researchers wrote.

The study was published in November in the journal Sleep.

Live Science