Hello crips
I dont know but it may be that your father is suffering from 'delirium' which appears to be quite common in elderly people admitted to hospital (and existing dementia is one of the risk factors for developing delirium). These NICE guidelines may be worth reading:
http://guidance.nice.org.uk/CG103/PublicInfo/doc/English
As Margaret W has said, it may just be the stress and change of scenery that has triggered this. But like lin1 and alfjess have mentioned, its worth investigating other possible reasons such as changes in medication etc. Has he had a CT head scan to rule out any vascular changes in the brain? - it may be worth asking the staff about this.
I see that you say its not a UTI, which is often a cause for acute confusion. 'Little' things like making sure your father is not dehydrated are important as well.
My father was diagnosed earlier this year with Alzheimers. The reason he ended up having tests for dementia was because we noticied he was depressed for several weeks (we had not noticied any major memory problems at all - he just seemed to be finding it hard to cope so much with things like financial issues - but we put it down to him feeling low in mood) and then suddenly out of the blue he became very confused which was completely out of character. It started when he told me he'd put the electric kettle on the stove and it went on fire. Then over a course of two weeks he was sometimes forgetting where/who he was, could not read a clock, and was getting night confused with day.
It was EXTREMELY distressing. So I know how you must be feeling. He didnt have a UTI and all his blood tests were normal, except for his prostate level (it was through this we found out he had prostate cancer). He had CT head scan, and ultra sound scan on neck (to check the blood vessels through to brain). I was convinced he must have had some kind of mini stroke that had triggered vascular dementia. But it turned out there was no vascular changes. The CT head scan showed some other changes and linked in with his behaviour they diagnosed Alzheimers. However, that period of acute confusion did wear off. My dad isnt the same man he was at all but he's able to cope day to day. If you spoke to him and didnt know him you wouldnt think there was any problem.
I was all such a confusing time and I still find it hard to get my head round it all. This piece of information comparing delirium, dementia and depression may be helpful to you:
http://www.dhmc.org/dhmc-internet-upload/file_collection/3ds_features.pdf
As lin1 says - dont wish to worry you with all this info. But I think its best to try and find out as much as you can so you can question the hospital staff so that all is being done to investigate your fathers change and to ensure his care is managed effectively.
I really hope your dad feels better soon and that he is back home soon.
Take care