What’s wrong with my girl? (shaking/pulsing)

Hi all! The rat on the top is 6 months old and about a month ago she randomly would start shaking like this, but would stop after about 20 seconds. I figured it was just a weird rat thing, plus she’s been eating like mad and been very active lately. Last night she was her normal energetic self, but today she’s been like this consistently. She’s moving around the cage occasionally, but not eating or drinking when offered. I’ve contacted an emergency vet, but I’m not sure what it is and what I can do for her. Any advice is appreciated ❤️