What Do People Say When They Talk in Their Sleep?

There's a persistent idea that sleep talking is a kind of truth serum. The guard is down, the filter is off, and whatever comes out must be what someone really thinks. It shows up in sitcom plots, in anxious jokes between new partners, and in a surprising number of search queries asking whether a partner's sleep talk "means something."

When researchers finally sat down and transcribed a large amount of it, what they found was much stranger and much less incriminating. The sleeping brain mostly says no, swears a lot, and leaves polite pauses for someone to answer.

Most people have done it

Sleep talking is one of the most common things a sleeping body does. Surveys put lifetime prevalence somewhere around 60 to 66% of adults, and it's far more frequent in childhood. Somewhere between half and most young children talk in their sleep at some point, and it usually tapers off through adolescence.

The regular, most-nights version is rarer. The American Academy of Sleep Medicine puts it at around 5% of adults, and on its own it's considered harmless. If you've been told you talk in your sleep and nothing else is going on, you are in the majority, not the exception.

The study that actually wrote it all down

The best look at what gets said comes from a 2017 paper in the journal Sleep by Isabelle Arnulf and colleagues at the Pitié-Salpêtrière hospital in Paris. They recorded 883 speech episodes from 232 people during video-monitored sleep and transcribed everything that could be understood.

One caveat before the numbers, and it matters. Most of those 232 people were sleep clinic patients: 129 with REM sleep behavior disorder and 87 with sleepwalking or sleep terrors. Only 15 were healthy sleepers. Those are exactly the people who talk the most in their sleep, which is why they were useful to study, but it means the results describe heavy sleep talkers more than the occasional mumbler.

With that in mind, here's what came out.

59% of the utterances were not words at all. Mumbling, laughing, crying, shouting, whispering. Of the speech that could be transcribed, the single most frequent word was "no," and negations made up 21.4% of all clauses, several times their rate in waking conversation. Profanity turned up in nearly 10% of clauses. The f-word in particular appeared around 800 times more often than it does in normal speech. Men talked more than women and swore more when they did.

So far that sounds like the truth serum theory with extra swearing. The next two findings are what undo it.

It's one side of an argument

The speech was grammatically correct far more often than you'd expect from a person who is unconscious. And it had the rhythm of dialogue. When sleepers paused, the gaps matched the pauses people leave in waking conversation when the other person is speaking. They'd say something, wait roughly the length of a reply, and respond.

There was no other person. The most natural reading is that the sleeper was answering someone in a dream, and what the microphone caught was half of an exchange whose other half only existed inside their head.

That also explains why so much of it was hostile. The researchers noted that the content skewed toward conflict: refusing, insulting, condemning, telling someone off. That lines up with a long-running idea in dream research that a lot of dreaming involves rehearsing threats, and a dream argument is exactly the kind of scene where "no" would be the most useful word you have.

Which is why the confession theory doesn't hold up. What you're hearing isn't the sleeper's hidden opinion about the room they're in. It's their lines in a scene you can't see, addressed to someone who isn't there.

Some people are much more interesting at night

The extreme cases make the point better than any statistic.

In the 1960s, the New York songwriter Dion McGregor had a roommate who started taping his sleep talk. The result was around 500 recordings of long, fully narrated monologues in different voices, including a game of roulette played with poisoned eclairs. Decca put out an album of them in 1964, with a companion book illustrated by Edward Gorey.

More recently, Karen Slavick-Lennard kept a log of what her husband Adam said in his sleep, a mild-mannered Englishman whose nighttime self turned out to be arrogant, crude and weirdly fixated on lentils. It became a popular blog and then a book, Sleep Talkin' Man.

Nobody listening to either of them concluded they were hearing hidden truths. They were hearing a narrator deep in a story. Awake, both men were by all accounts nothing like their sleeping selves, and that's rather the point.

How to use your own sleep talk

If you live alone, or nobody has ever mentioned it, you probably have no idea whether you talk in your sleep. That's a gap worth closing if you keep a dream journal, because sleep talk is one of the only records of a dream made while the dream is still happening.

The method is simple. Put your phone on the nightstand with a sleep talk recording app, the kind that only saves audio above a volume threshold so you're not scrolling through eight hours of silence. Do your journal entry first thing, before you listen, exactly as you normally would. Then check the recordings and compare.

Three things tend to come out of that comparison. Sometimes a recording drops you straight back into a dream you'd completely lost, which is useful on mornings when you wake with nothing. Sometimes it contradicts what you wrote, which is a small lesson in how much reconstructing your memory does between waking and writing. And over a few weeks, you get a sense of what your own dream arguments tend to be about, because if the Arnulf data holds, you probably do have them.

Two practical notes. Recording anyone who shares your bed needs their agreement first, obviously. And if the recordings turn up shouting or thrashing along with the talking, or you're older and it started suddenly, that's worth mentioning to a doctor, since loud, violent sleep talking is one of the signs of REM sleep behavior disorder rather than ordinary sleep talk.

Otherwise, whatever turns up on the recording, don't read it as a confession. Read it as your half of a scene, and go looking for the other half in your journal.