Am I right to call 111?

I agree. Neighbour to begin with until you have take to think and take stock.
Don't be rushed into anything.

OP the cat will sleep so I think leave him where he is with a visitor feeding.

If there is a neighbour to help out I definitely think that’d be best for the cat for the next week or so, hopefully by Wednesday/Thursday you’ll have a bit more idea how things are going and can rethink cattery or a vacation at your house!

She’d be just as unknown to DM if DM had hired her. Perhaps you could lock a few internal doors.

This is another that may help, although I don’t know anyone that has used this one https://themayhew.org/how-we-help/in-our-home/pet-refuge/

There are charities for pets that might be able to help, this is one, someone local to me has a dog from cinnamon trust https://cinnamon.org.uk/

Cinnamon Trust can help with animal care whilst the owner is in hospital, or local rescue centres may be able to help - I'm thinking foster care for the cat, rather than someone visiting the home. Volunteers will be experienced at fostering animals.

A cat-visitor would be preferable to a cattery from the cat’s point of view. Keeps a bit of stability in his life. When we used one we put a supply of food and dishes in the porch, so we gave her a key for that but she didn’t have to get to grips with the burglar alarm. But that was only for a weekend

I also wouldn't be happy with someone going into my relation's house. They can nose around as much as they like, take what they want. I would go for a cattery, for now.

Actually both my in-laws had dementia. My mil lived with us for several months and my fil was in a psychiatric ward because of his level of paranoia. So I am totally aware of how stressful and devastating it can be.
But I have also been involved with probably hundreds of patients with dementia and the presentation can be very variable. And delirium is very common. And this sounds like delirium.
An argument between us is totally pointless to the op so I’m going to bow out here. I understand you are being supportive but you ar3 also being too definite. The outcome here is not clear yet

I understand, it just might be better for the cat. It’s difficult, I appreciate.
If you need a key safe on the door, local councils often fit them for free.

Would a neighbour pop in and feed him OP? I think I’d probably try bringing him to your house first if not.

I’m sorry you're going through this, the uncertainty is just awful. I hope it does turn out to be a UTI, but she does sound a bit like my friends DM who had Lewys bodies dementia, she went from fine to needing two carers at a time as she became so violent, virtually overnight.

Either way, she’s in the best place, there’s not much you can do, so use this time to decompress a bit and let the hospital do the worrying.

A local cat sitter may allow be able to help if a cattery can’t.

Putting her cat into a cattery for now sounds like a good idea. But don't tell your DM you have! Say you're visiting it daily, or whatever.

I'm not. (She said, argumentatively.)

You've just literally posted what I've been saying.

This may not be due to the infection. It could be a deterioration in her dementia.

Until she's moved to a more suitable environment there may not be an improvement. Has she had any medication to calm her down?

@JamieFrasersSassenach i’m so sorry that your dm hasn’t improved. Relief from the constant state of alert must have felt tantalising close. Please try not to carry the weight of being responsible for her entire happiness. The situation is awful but you don’t have a magic wand and you can only make decisions and support her within the constraints of what’s available.

I think I would be getting into the habit of phoning the ward before making any journeys there, ideally speaking to her over the phone if the nurses judge it to be of any benefit. They’ll blatantly see that you clearly care for her and that you aren’t abandoning her.

Is it likely your work will be supportive of you if you explain the situation and the unknowable nature of when you’ll likely be needed?

However, this may be useful in securing further support for her. Obviously the immediate priority is to get any infection dealt with but it does also flag up her needs to be prioritised by a discharge team.

@BigFluffyHoodie why are you being so argumentative?

I'm sorry that there's been this sudden and worrying change in your mother's condition, OP.

This may not be due to the infection. It could be a deterioration in her dementia.

Until she's moved to a more suitable environment there may not be an improvement. Has she had any medication to calm her down?

I can certainly know the present. And the present is that an NHS ward will do all they can to discharge a patient - two days ago a doctor said OP's mother was medically fit to be discharged. This morning there is a security man sitting on her bed. I did warn the OP about unsafe discharge. Luckily there hasn't been one here, but only because the ward sister is more clued up than the actual doctor.

The way that the OP's mother is currently responding is exactly as I predicted. Ironically I held off mentioning the possibility/inevitability of her being sectioned, as I didn't think OP was ready to hear that. One day later, that is now an expected development.

What I am doing is saving the OP time and emotional energy.

And @RunnerDown - you even said it yourself.

Because dementia is ( usually) a slowly progressive illness

If it was always slow, you wouldn't have need to put "(usually)", would you?

None of us can know the future for the OP's mother.
We're not there and we're not treating her.
Of course it's tempting to compare to our own experiences but people are individuals and there is often big variations in how they respond to situations and illness . And dementia.

You are used to one side of dementia. I have seen the other.

People always think it "came on quickly" and are shocked, so it must be delirium. Whereas, the person has been declining into dementia and it has only just become unignorable, because there has been a crisis. When people around them such as friends and relatives think back, they start connecting the dots and realise that there was a much longer onset than originally occurred to them.

My posts, while seeming "aggressive" to you, are just trying to help the OP not waste weeks of mental, physical and emotional energy trying to deal with a condition that is further progressed than they realised. And so far, my posts have been accurate.

Because dementia is ( usually) a slowly progressive illness. And the op describes a sudden deterioration in both her mums level of confusion, along with the development of paranoid delusions and aggressive behaviour. There is evidence of a UTI. Delirium presents acutely - and is secondary to some kind of physical insult.
Of course you can have paranoid delusions and aggression in dementia but it tends to not develop quite so acutely. And I am not saying that the OPs mum doesn’t have dementia - she may well have underlying dementia .
But you cannot make the statement that this is the new normal. Because you don’t know that . No- one knows the level of recovery there will be for the Op’s mum.
I find you posts aggressive @BigFluffyHoodie and I appreciate you are trying to support the op. But you are letting your own experiences colour your judgement.
I also worked in this area for over 30 years