Uncontrollable Laughter is an illness symptom in DayZ that presents after consuming human meat.
This symptom appears when you contract Brain Prion Disease from eating human steak or human fat, causing the afflicted player to audibly laugh at random intervals. Making you crazy and insane. There is no way to prevent this laughter and it can easily give away a hiding Survivor. Since Brain Prion Disease is incurable, the associated uncontrollable laughter will occur for the remainder of the afflicted's life. The only cure is death.