Thanks Naomi - sort of helps to know that it might be regression related as I get so hung up on finding the reason for things and fiddling with her routine, which I don't think helps. I medicated last night and comforted as necessary and she was trying to settle, but just couldn't seem to get comfy.
She was super tired this morning, and unless she woke up much earlier than I thought (always possible but I don't think so this time), then she could handle a much shorter A to her nap than usual. She was falling asleep in her buggy and crying, which is most unlike her (pretty much never fell asleep in her buggy even as a newborn). Put her down for a nap now but suspect she will short nap me.
The more I think about it, the more I think I should move to set naps - the guessing about her WUs etc is driving me mad and I think life might just be simpler. She's 18 months so should be able to cope by now, no?