Pseudobulbar Affect is characterized by sudden, frequent, uncontrollable fits of laughter or crying. These bouts don't match the emotion one feels (e.g., uncontrollable crying but not sad or uncontrollable laughing but only slightly amused). Bouts of crying are more common and may turn into bouts of laughter, or vice versa, and these episodes last minutes.
People who have PBA have an underlying brain condition or neurological injuries, including stroke, amyotrophic lateral sclerosis (ALS), multiple sclerosis (MS), traumatic brain injury, Alzheimer's disease, and Parkinson's disease. Since neurological diseases are not always a visible disability known to others, you may not be able to discern why someone is behaving so outrageously. This may cause onlookers to jump to conclusions that someone is mentally ill, immature, or rude.