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Hi all, thanks for your replies,
She took the cat to the vet first thing in the morning yesterday, and they said from how she described it, it is epilepsy, but as it is only the first fit, they wont be giving the cat any medication unless it happens again.
She was amazed by how, when she had put the cat in a dark room to rest, her other 2 cats just sat either side and watched over the cat, as if keeping an eye on her & making sure she was fine :)