My dog shivers, pants, acts scared, hot body, cold paws. What's wrong?

I can certainly see how this would be very alarming to witness. The symptoms you describe may be related to a disease process affecting an organ system (more often the neurologic (seizure event) or cardiac (heart event) systems). What i would recommend is a visit to your family veterinarian for a physical exam, to discuss the events, and to discuss additional testing (like bloodwork to rule out organ changes). It is also extremely helpful to get a video of an event so that your vet can watch it. Also, given the age of your pup, make sure there is nothing new in the environment that he could be snacking on that may be toxic to dogs (plants, etc.). I hope this helps and thank you for using Petco Pet Education Center, formerly Petcoach!