I am booking her in to the vet's.
Meanwhile, any ideas? She is a normal shorthair, 7 years old, always been a bit of an indoor wuss but has access to outside.
We noticed last night she was being fairly quiet and napping a lot by the radiator in her catbed. She did enjoy her food this morning though, and got up for it enthusiastically, and went outside to pee. But she seems unsteady on her back leg(s). No visible injuries, and she lets me cuddle her without showing any pain.
Thanks for any advice.