Will Falconer, DVM Moderator
The commonest is the most worrisome: out back, someone "discovers" this dog is "out of date" on vaccinations, and does you the "service" of bringing her up to date. And, a month later, you've got allergies or seizures or ADD behavior.
Not suggesting that happened to your dog, as you would most definitely have been billed for it. More likely "caught a bug," and got over it.
Just good to be aware, and act like Destiny does: never out of sight.