In a psychological context, "labile mood" refers to a mood state in which a person experiences wild, uncontrolled mood swings. Labile mood is also known as labile affect, emotional dysregulation and pseudobulbar affect. The mood state is linked to several mental illnesses, including bipolar disorder, schizophrenia and borderline personality disorder.
Someone in a labile mood exhibits an exaggerated, inappropriate emotional reaction in response to normal stimuli, such as sobbing over a dropped plate. Someone experiencing emotional dysregulation may also demonstrate a strong, opposite emotional reaction, such as uncontrollable laughter after getting into a car crash. Exaggerated emotional responses that do not match the situation are called mood-incongruent.