Hello @mvanstem, Welcome to Connect. I'm sorry they couldn't work an appointment in during your last visit.
Rochester Mayo Clinic has a great Ophthalmology department but it can be a waiting period to get an appointment due to the number of patients trying to get appointments. I had cataract surgery for both eyes at Rochester Mayo. Here's some information that covers how it's diagnosed and more:

--- Nystagmus: Definition, Causes & Treatment:
https://my.clevelandclinic.org/health/diseases/22064-nystagmus
You mentioned you are weighing whether you should go back for testing. Are the tests to confirm your diagnosis and possible treatments?