Thank you all for your wise words, it's so nice to know I'm not alone in feeling like this. It all seemed such a surreal experience from when I got the call to say my daughter had started her labour to when I got back home after the birth. I caught the train from the Midlands to London as soon as things started, a crack of dawn journey; husband away working; dog very old and sick needing to be taken into the kennels; medicine to be picked up from the vet - the usual chaos, but so exciting and I was so desperate to get there. Then three days later back on the same train, wearing the same clothes, reading the same page in my book, house as untidy as I left it, dog still ill, husband still away, nothing had changed and yet everything had changed.
I'm sure I'll come round eventually, I think it was a bigger shock than I had anticipated seeing my child with her own child.