I am having a hard time understanding exactly what you are saying.Is he shaking only when he goes in the car with you or just all the time? If he is doing it after what I thought seemed to be a horrible vet experience than I guess it is understandable that he is nervous. If he is not acting normal and shaking all the time I think I would take him to a different vet and see what they say. I just thought the whole vet visit sounded sketchy. My 3 go in and out all day into the AC and they do not get sick, I have NEVER had a dog get sick from that. Not in 25 yrs of owning dogs. This is just my opinion however,you have to do what you feel is best for Spanky. Oh and I think it is highly unlikely it has anything to do with his hormones. Good Luck and keep us posted, I hope he gets back to his normal self soon
Again that is just my opinion.
BTW, How big is Spanky? He sounds a little old for hypoglycemia unless he is a tiny and even then you say he is eating and drinking normally? Is he going to the bathroom normally too? Just thought I would ask..