Man in his 60s with dementia?

My FIL, in his 60s, currently lives on his own in the basement of a home that my husband owns (long story). Apparently last night, he fell asleep at 6/7 pm, then woke up at 11 pm and thought that it was 11 am. He texted his sister to tell her he missed his haircut appointment (which was early this morning). She was asleep at this point and didn't answer. He called her a few hours later at 2 am, then at 4 am, thinking it was the middle of the day. His sister picked up at 4 to let him know it was actually 4 AM and not PM...and he kept thinking it was 4 PM "because it's winter and it gets dark early now." When he's convinced that it's actually the morning, he goes to his hair appointment and then is supposed to come over to my husband's and my house for lunch later. When he gets here he gets lost close to the house and keeps passing it, even though he's been here before, although only like 3 times because we just moved a couple months ago. He passes the house even as my husband is outside signaling to him (he doesn't see him)...My husband finally gets him in the house. At this point my husband and I have decided it would be a good idea for him to be taken to the hospital. He starts telling us what happened and how he got confused and I'm having trouble telling what is normal and what isn't, since my FIL is not totally with it as it is. My husband thinks it isn't normal though. My FIL then says that he thinks it's because he's living in the basement and this threw off his circadian rhythm because he can't see the sun come up or go down (?)...that he needs to be more active and have a schedule (meanwhile we are pretty sure he spends all of his time sitting on the couch watching TV, and probably drinking more often as well as of late, and he's clearly barely even looking outside).

My FIL has a history of at least 1 stroke and brain surgery in the past because of a tumor. Ever since then his family says he hasn't been quite the same (I wasn't around at this point). Recently he spent two weeks around Thanksgiving quarantining because of COVID. We saw him after Thanksgiving, on Tuesday, and my husband thinks he seemed like he was wasted and maybe slurring his words.

My husband has been in the hospital with him all day. Blood work all looks good. I think they have ruled out a stroke at this point but I'm not sure. They are waiting for results of a CAT scan but I am curious of people's experiences here with situations like these. I just think he is relatively young to be experiencing something like dementia...although with his brain health history I am not sure how it affects things. And if he is with it enough to recognize he thinks he needs more exercise, sunshine etc then why isn't he doing something as simple as going for a walk around the block? Maybe depression? I know he's not really concerned with COVID so I don't think that's a factor for him at least with not going outside. I guess I'm just thinking out loud here and seeing what other people have experienced.