Another one that is possible is hyperthermia or heat stroke
. It may have been hot in the garage and the dog
could get heat stroke
stuck in a hot unventilated area. Of course, your dog's illness may be unrelated to the garage episode. If unrelated, there could be many possibilities, such as: back pain from disk disease, pain from other causes, such as a soft tissue injury, Lyme or other tick borne disease, dietary indiscretion causing GI discomfort and many more...