I've heard dogs find zooming as a way to get out of the moment, and it's most common when they're stressed out. My dog used to have the zoomies at agility a lot, but I gave him some time to individually meet each dog and play with them which seemed to help ease up the stress. Since then, he doesn't seem to have any more stress zoomies and only the occasionally, "Let's go crazy!" terrier zoomies! 