My dog started shaking and lost balance while watching me eat?

[tiz]

During breakfast, my dog was watching me as usual in the hope of getting some crust, and suddenly the upper half of her body and jaw shook for a few seconds and she lost balance whilst sitting and stumbled over. This happened again just now while I was eating an apple, except it lasted longer and was a bit more violent. She is pretty old, god love her, but what does this mean? I'm booking in for an appointment with the vet, but won't be able to get in until next week. Last week, she also had a short stint where all day, her jaw was clenched and shook really badly, like they were chattering. Again, it only seemed to be when I was eating food. What's causing this? Was what happened classified as a fit? I'm scares for her.