Had my 13yr old Jack terrier to vet for kidney issues this week. She changed diet to Purina Kidney diet and prescribed Proin for incontinence, and enalipril for high blood pressure. Seemed fine on meds, but today is vomiting, shaking, and falling over. Is this reaction to meds and change of diet? :(

It sure could be. I lost a dog to a drug reaction earlier this year. I have no experience with those drugs in particular but I would be inclined to the drugs rather than the diet as the culprit. It might be something completely unconnected to the meds and the diet but with the timing it would be a heck of a coincidence. I would get ahold of that vet immediately and let her know what is going on. This could easily kill your dog especially at his age.