sundowning

noun

sun·​down·​ing ˈsən-ˌdau̇n-iŋ 

: a state of increased agitation, confusion, disorientation, and anxiety that typically occurs in the late afternoon or evening in some individuals affected with dementia

Sundowning is a major problem in the middle and late stages of disorders, such as Alzheimer's disease, that cause dementia.

—Patricia N. Prinz et al., The New England Journal of Medicine