"Sundowner’s Syndrome"

"Sundowner’s Syndrome is the name given to an ailment that causes symptoms of confusion after “sundown.” 

These symptoms appear in people who suffer from Alzheimer’s Disease or other forms of dementia. Not all patients who suffer from dementia or Alzheimer’s exhibit Sundowner’s symptoms, however. 

Conversely, some people exhibit symptoms of dementia all day which grow worse in the late afternoon and evening, while others may exhibit no symptoms at all until the sun goes down."...

link: http://sundownerfacts.com/sundowners-syndrome/