Paradoxical laughter is an exaggerated expression of humour which is unwarranted by external events. It may be uncontrollable laughter which may be recognised as inappropriate by the person involved. It is associated with altered mental states or mental illness

Mental illness

A mental disorder or mental illness is a psychological or behavioral pattern generally associated with subjective distress or disability that occurs in an individual, and which is not a part of normal development or culture. Such a disorder may consist of a combination of affective, behavioural,...

, such as mania

Mania

Mania, the presence of which is a criterion for certain psychiatric diagnoses, is a state of abnormally elevated or irritable mood, arousal, and/ or energy levels. In a sense, it is the opposite of depression...

, hypomania

Hypomania

Hypomania is a mood state characterized by persistent and pervasive elevated or irritable mood, as well as thoughts and behaviors that are consistent with such a mood state...

 or schizophrenia

Schizophrenia

Schizophrenia is a mental disorder characterized by a disintegration of thought processes and of emotional responsiveness. It most commonly manifests itself as auditory hallucinations, paranoid or bizarre delusions, or disorganized speech and thinking, and it is accompanied by significant social...

, and can have other causes.

Paradoxical laughter is indicative of an unstable mood, often caused by the pseudobulbar effect, which can quickly change to anger and back again, on minor external cues.

This type of laughter can also occur at times when the fight-or-flight response may otherwise be evoked.