Laughing during sleep, also called hypnogely, is a relatively common occurrence. It can often be seen in babies, sending parents scrambling to note down baby’s first laughter in the baby book!

In general, laughing in your sleep is harmless. In rare instances, it can be a sign of a neurological issue.

Understanding sleep is important when looking at laughter during sleep. There are two main kinds of sleep: rapid eye movement (REM) and non-REM sleep. Over the course of a night, you go through multiple cycles of REM and non-REM sleep.

Non-REM sleep occurs in three stages:

  • Stage 1. This is the stage where you go from being awake to being asleep. It’s very short. Your breathing slows down, your muscles start to relax, and your brain waves slow down.
  • Stage 2. This stage is a time of light sleep before the later deeper sleep. Your heart and breathing further slow, and your muscles relax even more than before. Your eye movements under your lids stop and your brain activity slows down with sporadic periods of electrical activity.
  • Stage 3. You need this last stage of sleep in order to feel refreshed. This stage occurs more in the first part of the night. During this time, your heartbeat and breathing are at the slowest point, as are your brain waves.

REM sleep is when most of your dreaming occurs. It first starts about an hour and a half after falling asleep. As the name suggests, your eyes move very quickly back and forth under your eyelids. Your brain waves are varied but are close to how they are when you’re awake.

While your breathing is irregular and your heartbeat and blood pressure are similar to when you’re awake, your arms and legs are temporarily paralyzed. This is so that you don’t act out the activity you may be doing in your dreams.

Laughing in your sleep usually happens during REM sleep, although there are instances of it occurring during non-REM sleep, too. Sometimes this is referred to as a parasomnia, a type of sleep disorder that causes abnormal movements, perceptions, or emotions that happen during sleep.

Laughing in your sleep is typically nothing to worry about. One small 2013 review found that it’s most often a harmless physiological phenomenon that occurs with REM sleep and dreaming. While it can happen during non-REM, this is much rarer.

REM sleep behavior disorders

Rarely, laughter during sleep can be a sign of something more serious, such as REM sleep behavior disorder. In this disorder, the paralysis of your limbs doesn’t occur during REM sleep and you act out your dreams physically.

It can also include talking, laughing, shouting, and if you wake up during the incident, remembering the dream.

REM sleep behavior disorder may be associated with other disorders, including Lewy body dementia and Parkinson’s disease.

Parasomnia

Laughter in sleep can also be associated with non-REM sleep arousal parasomnias, which are somewhat like being half-asleep and half-awake.

Such parasomnias include sleepwalking and sleep terrors. These episodes are on the shorter side, with most lasting less than an hour. These are more common in children, but they can also happen in adults. An increased risk of parasomnia can be caused by:

It’s not entirely clear what causes a baby to laugh in their sleep. We don’t know for sure whether babies dream, although they do experience an equivalent of REM sleep called active sleep.

Since it’s impossible to really know whether babies dream, it’s believed that when babies laugh in their sleep, it’s often a reflex rather than a response to a dream they’re having. For example, many researchers note that babies may twitch or smile in their sleep during active sleep.

When babies go through this type of sleep, their bodies can make involuntary movements. These involuntary movements might contribute to smiles and laughter from babies during this time.

In very rare instances, there are types of seizures that can occur in infants that cause episodes of uncontrolled giggling, called gelastic seizures. These are short seizures, lasting around 10 to 20 seconds, which can start in infancy around 10 months old. They can occur as the baby is falling asleep, or while they’re asleep it might wake them up.

If you notice this happening regularly, multiple times a day, and accompanied by a vacant stare, or if it happens with grunting or unusual bodily movements or squirming, talk to your pediatrician.

Diagnosing this condition can be tricky, and the doctor will want to know more about the situation and possibly run some diagnostic tests to be sure of what’s going on.

While there are instances where laughing in your sleep can indicate something serious, in general, it’s a harmless occurrence and you have nothing to worry about.

For babies and young children, laughing in their sleep is typical and generally not a cause for concern. This is especially true if it’s not accompanied by any abnormal behavior.

If you’re experiencing sleep disturbances or issues with sleeping, it’s worth talking with your doctor about your concerns. They may refer you to a sleep specialist for further evaluation.