Thank you for your advice.
I don't think it is viral... I've had all of these rats for well over a year now and none are showing signs.. With chemicals, again, nothing new and no others are showing issues, so I am guessing that it has to have been either trauma (him falling badly etc.) or a tumor or stroke maybe?

Unfortunately, we don't own a gun and live in the city with close neighbors...Or that would be a good option. I saw a video on how to do a Co2 euthanasia with vinegar and baking soda (slowly with a funnel). I may do that if I have to. I have all of the supplies on hand except for tubing.

The suddenness of this is what bothers me. He showed no symptoms yesterday.