Think of your tongue as a relaxed houseguest during sleep. When you’re in deep REM, your muscles—including that big, versatile muscle in your mouth—go limp. This relaxation can cause your tongue to drift backward or to the side, right into the closing arc of your teeth.
Add a sudden jaw clench, a nocturnal grind (known as bruxism), or a vivid dream where you’re chomping on an imaginary steak, and you’ve got a recipe for a painful wake-up call. A 2017 study in the Journal of Oral Rehabilitation found that stress and poor sleep quality significantly increase the frequency of involuntary jaw movements, making tongue bites more likely.
Culturally, we’ve always given this phenomenon a mystical gloss. In Chinese folklore, biting your tongue in sleep is said to mean someone is thinking about you—a flattering, if painful, sign of desire. Meanwhile, some Native American traditions interpret it as a warning to watch your words the next day. Fun fact: Victorian-era parents sometimes blamed it on “bad dreams from a heavy supper.”
