I am terribly sorry about the non recognition. Like you and like the other posters who have voiced their compassion, I hope that it was a momentary loss. Forgetfulness can be a sometime thing!
It’s odd that being aware beforehand of this likelihood in no way eases the profound shock and dreadful pain when it does. My OH worked for eight years, until late last year, on a book he will now not be able to publish, such has been his decline since then. Two or three months ago, he came to me holding the typescript (massive, about 500 pp.) - and asked me if I knew what it was.
I had “known” this moment might come but was still devastated when it did. And this was a minor incident in comparison with what you experienced with your mother not knowing you. Again, I am so sorry, dear Jezzer.
Reading all that has been said in response, I can only add that I think we all have to be really gentle not just with each other, but with ourselves. We MUST recognise how hard this, is in order to be able properly to look after ourselves.
Sorry I am just thinking aloud here. Example: tea and chocolate biscuits in bed is NOT how I should be caring for myself right now! I tell myself at least it’s not vodka in this teacup - but I need to do better than this!