Dear Hugh
I don't know whether you are getting any help or support from other sources - have you got a CPN (Community Psychiatric Nurse) and/or Social Worker allocated to your mother. I looked after my husband for some years, and the CPN was a great source of practical and moral support and advice. The Social Worker was not quite so helpful, but did get the Care Assessment of my husband's needs and a Carer's assessment done for me (you are entitled to these, by the way) - a first step in getting things like respite or day care. I understand from previous postings on this forum that it can be the other way round, Social Worker good, CPN less so, but your mother's GP or Consultant should refer you to these services.
Also there are voluntary organisations that can give advice or provide a sitting service so that you can at least have short breaks. Your local Alzheimers Society branch should be able to put you in touch with these.
At the very least, do keep in touch through this forum - it was a real life-saver for me, as you can ask anything or just sound off when it all gets too much, and everyone will understand, as we have also been there.
KInd regards
Ruthie