Glad to hear your dog is doing better.
Dogs don't seem to tolerate high temperatures as well as we do.
Signs of heat stroke in dogs usually include rapid breathing, bright red gums, and a high temperature. Also you can see vomiting
Then the dog can become unsteady and stagger which "might" have been what you saw. Mild cases respond to moving the dog to a cooler surrounding, such as an air-conditioned house.
Good luck
Chris