Hi Jackie
Like your dad, my dad has dementia too and has also had a very sharp decline recently. He lives at home with mum and she is also finding it quite hard at times to cope with him, its not knowing how to deal with him. It has been a shock to us all how quickly he has changed.
He is worse at night times and sometimes during the day, has trouble remembering who mum is and where he is (has been for the last 40 years. Like yourself we too tried to make him see that what he was saying was wrong and/or tried to convince him that mum was MUM and not some stranger who had just dropped in, but he just became more and more agitated and angry. Reading through posts and listening to advice on TP I decided to try and go with the flow even though i felt like we were betraying him in some way, but I have to be honest and say that from his point of view he is much happier when we agree and quite often the repeating of the question/conversation will stop there once we have agreed, ending in a much less stressfull time for all. Sometimes when he's going on and on though, i try not to participate too much in his conversation and try to change the subject completely. I have a two year old who my dad adores and quite often I can say things like 'Daniel, ask Grandad to help build your bricks or show grandad your book' changing the subject and giving dad something else physically to focus on.
One thing that we have found particularly useful, is, when dad is agitated at night, mum will play music that he likes, we have found that more often than not this will calm him down enough to make the whole situation more bearable. If he wakes in the night with his barrage of questions and accusations mum puts the cd back on and he settles back down quicker than he was before.
We have yet to have contact with the social services, this is a whole minefield which i am not looking forward to one little bit, to be honest i dont think i would know where to start but we'll cross that bridge when we need to and im sure there will be useful advice here to help.
Mum actually left a note for dad's doctor on Monday to try and see if there is anything that he can be prescribed to try and calm him down when he gets into one of his 'moments' several times lately i have seen him lose his temper, even to the point where he nearly threw a 'maraca' you know one of those shaker thingies at mum. My heart was in my mouth!!! We are waiting to hear what the outcome of this letter was. She finds it difficult to discuss anything with dad by her side and he (as far as we know) is unaware of the severity of his dementia.