my grandfather can't tell what time it is

Hi.  My grandfather is starting to scare us.  Everytime he sleeps/naps , it's like his body clock resets.  When he wakes up he thinks it's morning, goes for a shower, shaves etc.  as a result he ends up showering 3-4 times a day and asks for breakfast at all times, like 12 am.  he needs to be convinced that it is not morning.  this is affecting his taking of medication for high blood pressure as well as his eating habits (e.g. always would drink milk before sleeping, now refuses to have it, because he doesn't drink in the morning).  He has also begun to eat much more often and developed more of a sweet tooth.  he is 85, with no history of diabetes or any other illness, other than high blood pressure which has come about in the last ten years.  he has always been extremely fit with regular morning excercises and walks for 1 hour, mentally acute (he worked until the age of 75) etc.  Aside from his lapse of understanding of time, he seems normal.  what could this be?

[LLWB]

It could be beginning senility , cognitive function disorder, or alzeheimer's. He needs further testing to know.