A state of agitation or confusion, especially in elderly patients suffering from Alzheimers disease or other forms of dementia, which begins daily at nightfall and which is alleviated by daylight.
Nocturnal delirium of the senile patient is primarily due to the fact that the severe retention defect, and more particularly the greatly accelerated secondary elaboration (Cameron, 1940) found in senile patients, does not permit of the preservation of the spatial image after darkness has interfered with direct visualization.
Wikipedia foundation.