My son almost 7 has begun laughing in his sleep
When it occurs, I think it only lasts a few sexonds. I will often wake him and ask what’s funny and he has no recall and falls back asleep.
It is a benign phenomenon.
I read your question carefully and I understand your concern.
The phenomenon of laughing during sleep (the medical term is hypnogely) is a common phenomenon occurring in many people, usually during the dreaming stage, REM sleep, although not necessarily related to good dreams. While its mechanism is not well known, you can feel assured that it is benign phenomenon, it is not a manifestation of a more serious pathology. So unless there is awake abnormal laughing or other symptoms, there isn't any need for medical visits or tests, nor is any treatment needed.
I remain at your disposal for other questions.
Thank you for the follow up. I understand that reading about pontine gliomas has caused some alarm. It is true that neurological lesions like pontine gliomas, but also others such bilateral hemisphere lesions (from stroke, multiple sclerosis), motor neuron disease etc may manifest with pathological laugher. However it is not in isolation, even when there aren't signs like ataxia, motor deficits etc, there are some behavior changes and also the episodes are not manifested exclusively during sleep. That is why I still think that if there aren't other changes I do not think there is any brain lesion involved.
That is not to say that it is normal, it is considered a sleep disorder, but a benign one not something which is related to an identifiable lesion which would entail any risks. It is similar to sleep talking. Like sleep talking it may be an indication of a higher risk of developing REM sleep behavior disorder (acting out dreams - a complex of symptoms like talking, laughing, kicking, shouting during dream phase) or parasomnias such as sleep walking or night terrors (but a higher risk doesn't mean they will necessarily develop, time will tell).
As for what would cause it....as for most sleep disorders the causes are not well understood, it is though to be a combination of different factors, genetic predisposition, stress, changes in sleep schedule being the most cited ones.
Distinguishing laughter as physiological or pathological is not done by duration or frequency. Pathological laughter happens in an awake conscious individual, is a laughter which is uncontrollable and not suited to the actual emotions. It doesn't happen only during sleep. If there is a lesion, a structural damage (whether a tumor, stroke or other kind) it would affect impulse inhibition and expression of emotions all the time not only during sleep. In addition to that as I said such conditions do not affect exclusively impulse control, there is involvement of other functions such as motor control, balance etc.
Sleep laughter episode duration may vary a lot, from seconds to minutes, usually occur in bursts and can be stopped by waking someone although it may take some seconds to do that and it is not necessary to do. There is no clear cut distinction, no abnormal threshold regarding duration or frequency of sleep laughter because being considered benign there are frankly not many studies and agreed definitions about how long the episodes last and how frequent it is in children or adults. Generally speaking 20-25% of pediatric patients have some type of sleep problem. They diminish with time, rarer as they grow up. There are some studies regarding sleep talking which have shown to be much more common in children, happens in about 50% of children at least once a year and in 10% it may manifest nightly. I am afraid I am not aware of any precise figures on sleep laughter, I tried to find some epidemiological study but I didn't find any as I said. While figures shouldn't be as high as sleep talking, it is common.