This review integrates multiple levels of evidence, including molecular circadian mechanisms (e.g., clock genes and melatonin signaling), neuropathological findings (such as suprachiasmatic nucleus involvement and α-synuclein deposition), animal and human studies, clinical motor and non-motor symptomatology, and therapeutic interventions (including light therapy, melatonin, and chronotherapy). It provides a focused analysis of circadian dysfunction and related clinical manifestations in patients...