As she stopped twitching she sat up and looked at me- I had gone to sit next to her- but she didn't "see" me, if you know what I mean? She then immediately ran to do her busies and then went looking for water. She was all nervous and wanted to come into the house so I let her and Thelma come in earlier than they usually do and made sure Louise was warm and comfortable.
I called the vet's emergency number and chatted to him, and given that she hasn't been sick in the last few days or weeks, epilepsy is the most likely culprit.
I then also chatted to him about what I'd seen over the last few months and I concluded that she must have had at least 4 seizures that I didn't see happen, I only saw her afterwards. And when I saw her face covered in white foam in November and concluded that she had suddenly come down with kennel cough again- even though I hadn't seen any other symptoms- it must have been soon after a fit. She salivates so much during a seizure that her whole face and neck is sopping wet, and I have seen her with a wet face on a few occasions and not known what caused it.
She hasn't had another seizure, but I will be taking her to the vet as soon as I can so that we can arrange tests and medication for her. The meds should prevent any more seizures.