It does sound like it was fear related and tiredness after all that anxiety would be normal.

In case this ever happens again one thing that will be helpful is if you learn to take a temp, have your vet show you how. There is a condition called hyperthermia which can be caused by anesthesia or extreme stress, which can cause the dog to overheat to the point where they start seizing or go into a coma and die.

My greyhound Maya is extremely fearful, after a vet visit and once home instead of calming down like she usually does , her panting continue to become faster and shallower and she started to look very very ill, having been in the past involved with a greyhound haul where one grey did overheat from stress and start seizing, and buckets of cold water had to be poured over him immediately, I realized then what was wrong with her and ran and grabbed a bunch of towels soaking them in cold water and threw them over her, it took about 20 minutes for her breathing to start normalizing and she was looking a lot better within half an hour and then she had a good long sleep.

In your case she was not that over stress and was able to cool herself down on her own, but having a thermometer on hand will let you know for sure if there is a potential for hyperthermia to occur and to know if you are going to have to help her cool down