Hypnogely, or laughing during sleep, is a common, involuntary occurrence. This involuntary expression of mirth can range from quiet giggles to loud, boisterous laughter. It is typically a harmless physiological event, affecting people of all ages, from infants to adults, and is generally not a cause for concern.
Understanding Sleep Laughter
Sleep laughter is a form of parasomnia, a category of sleep behaviors that occur during sleep, at sleep onset, or during arousal from sleep. Unlike conscious laughter, it happens without the sleeper’s awareness and is generated internally, often in response to dream content. The individual may not recall the dream upon waking.
This phenomenon is observed in both children and adults, though it appears more frequent in younger individuals. One study indicated that 33–44% of middle school children reported laughing in their sleep, and 73% of undergraduate students were aware of at least one such event annually. In babies, sleep laughter is often a sign of dreaming and is considered part of healthy nervous system development. It is usually a benign expression of emotions processed during sleep.
The Brain’s Activity During Sleep
Sleep laughter is closely connected to brain activity during different sleep stages. Most instances are associated with rapid eye movement (REM) sleep, the stage where vivid dreaming occurs. During REM sleep, the brain exhibits activity patterns similar to wakefulness, particularly in areas involved in emotion and memory processing. This heightened brain activity contributes to dream content that can trigger laughter.
The body typically experiences muscle paralysis, known as atonia, during REM sleep, which prevents individuals from physically acting out their dreams. However, vocalizations like laughter can still occur. While REM sleep is the most common time for hypnogely, it can also happen, though more rarely, during non-REM (NREM) sleep stages. The limbic system, including structures like the amygdala and hippocampus, plays a role in processing emotions, which may contribute to the emotional content of dreams that lead to laughter.
Emotional processing during sleep can manifest as laughter, allowing the brain to process and release accumulated emotions or tension from waking hours. The brainstem, which regulates many automatic functions during sleep, may also be responsible for the physical act of laughing.
When Sleep Laughter is a Concern
While sleep laughter is typically harmless, rare instances might indicate an underlying medical issue. It is important to distinguish between normal, occasional sleep laughter and more persistent or disruptive occurrences. In some cases, sleep laughter can be a symptom of neurological disorders.
One such condition is REM Sleep Behavior Disorder (RBD), where the muscle paralysis during REM sleep is absent. This causes individuals to physically act out their dreams, which can include talking, shouting, or laughing. RBD is more prevalent in older adults and can be associated with neurodegenerative diseases like Parkinson’s disease. Another rare neurological condition causing uncontrollable laughter is gelastic seizures, a type of epilepsy that may occur during sleep and can sometimes be confused with dream-related laughter.
Consult a healthcare professional if sleep laughter is frequent, disruptive, or accompanied by other unusual behaviors. For example, if the laughter is violent, causes physical movements, or leads to distress or injuries, it warrants medical attention. Seeking professional guidance can help determine if an underlying condition requires treatment.