A nurse is caring for an older adult who lives in a long-term care facility on the Alzheimer unit. Every evening around 5:00 p.m., the resident becomes increasingly agitated and more confused, a state that lasts throughout the evening. The nurse recognizes this behaviour as:

A. Personality disorder. Personality disorders are long-term patterns of behaviour and inner experiences that deviate significantly from the expectations of the individual's culture. The described behaviour is a specific pattern related to the time of day, not indicative of a personality disorder.
B. Dementia. While dementia is the underlying condition, the specific worsening of symptoms in the evening is known as sundowning syndrome. Dementia alone does not specify the time-related pattern of increased confusion and agitation.
C. Delirium. Delirium is an acute, often sudden change in cognition and attention, usually caused by an underlying medical condition or substance use. The described behavior follows a regular daily pattern, indicating a different issue.
D. Sundowning syndrome. Sundowning syndrome refers to increased confusion and agitation in the late afternoon and evening, commonly seen in individuals with Alzheimer's disease or other forms of dementia.