Q: I have a 2 year old nephew who laughs uncontrollably in his sleep. Could he be suffering from a type of epilepsy. A physician I know mentioned that it may be startle epilepsy. Have you ever heard of this?
A: Laughter, as well as other emotional behaviors, may occur as a manifestation of seizures. Their occurrence during you nephew's sleep do not necessarily mean that seizures are occurring, however. This can be easily sorted out with an overnight EEG study (not a "sleep study").
Startle epilepsy refers to a condition where stimuli that would startle a person (for example, a sudden loud noise) would also trigger a seizure. This does not appear to be what you are describing.