Lately my father has been really confused as to whether it's day or night. Will this pass, or only get worse?

Lately my 97 yr old father has really confused day vs. night. Will this pass, or only get worse? I thought it was just from a UTI, but the UTI is now over and he's still confused. I've bought him a clock with HUGE numbers, the day, the date and am vs. pm, to no avail. He also now sleeps fully clothed, no matter how much I try to get him to undress. Is this dementia or Alzheimer's?