What type of disease often arises without any known physical cause and manifests as behavioral or psychological symptoms?

A functional disorder refers to conditions where the physical structure of an organ or system appears normal, yet the individual experiences significant physical or psychological symptoms. These symptoms are often not linked to any identifiable physical cause, making the disorder challenging to diagnose through standard medical tests. Instead, the issues may arise from how the brain processes signals, how different body systems interact, or due to psychological factors. This is why functional disorders often present as behavioral or psychological symptoms.

Organic disorders, in contrast, are characterized by identifiable physical abnormalities that can be detected through imaging, pathology, or other medical assessments. Acute disorders refer to conditions that occur suddenly and are often severe but can possess identifiable causes. Subclinical disorders are conditions that exist but do not present obvious signs or symptoms. Therefore, the nature of a functional disorder aligns perfectly with the criteria of having no known physical cause while representing itself through behavioral or psychological symptoms.