Thanks for the information. It sounds like he may be having an issue with vestibular disease. This usually comes from the inner ear or brain. The vestibular system is responsible for controlling balance. I cannot rule out that this may be some type of seizure, especially with frequency of when it happens and the fact that he is better the next day. The problem is finding the cause of a vestibular or seizure issue. With the vomiting, a vestibular issue is more likely. As far as vestibular disease goes, an inner ear infection, overdose of metronidazole (an antibiotic), head trauma, middle/inner ear tumor or polyp, brain tumor and an inflammatory or infectious condition around the brain (encephalitis) are all potential causes. Some of these can be causes of seizures as well. The most common cause of vestibular disease is termed idiopathic, which means no known cause. We see it in geriatric dogs (usually older than your JRT). We usually do not find a cause with it, but it resolves in 1-2 weeks on its own. This doesn't really fit the bill for it. A toxin ingestion is possible, but it would have to be something he is continually getting into. The only rat poison that will cause neurologic issues are those that contain the ingredient bromethalin, which causes brain swelling, but it usually does not come and go. The other rat poisons cause blood clotting problems. The first thing I would do is get some blood work ran by your vet. They may recommend some imaging, such as x-rays, an ultrasound or even an MRI or CT scan. If the issue happens again before you can get him to the vet, I would try to get it on video, so you can show them the incident. That will go a long way in determining if it is a seizure or a vestibular issue. Please let me know if you have any other questions or concerns. Hope this helps.
My goal is to make sure that you get all your question answered and all the information you need. IF YOU ARE SATISFIED WITH MY ANSWER, PLEASE RATE IT. Rating it is the only way I get compensated for helping you, and we can still continue our conversation after rating. If you feel like it is not helpful to you, or if there is more information you need, please respond back to me before rating. Asking more specific questions usually helps a lot. Realize that our conversation is not intended to diagnose or treat a condition. There has to be a valid veterinary-client-patient relationship established with an exam, according to law. You should always follow up with your vet.