so very sorry had some real life rat emergencies to take care of so I missed your post.
Sudden and severe inner ear infection, could be head tilt, circling, falling over, nystagmus of the eyes (where they twitch).
In these cases antibiotics and steroids if possible are needed ASAP. If you cannot get steroids, giving NSAID's for a few days to combat the discomfort is better than nothing (Metacam/meloxicam or infant liquid ibuprofen)