If it does turn out to be the other thing, do two things before you ring anyone. Film it, because you will not be able to describe writhing versus tremors in a way that means anything over the phone and the vet will ask. And strip anything out that could be a toxin: change aromatic bedding, stop any treatment you started, open a window.
I overdosed a mite spray in 2022 and the twitching was the first sign. The vet's first question was whether I had video, and I did not.