I am praying, of course, that it's nothing serious. A sting or a bug bite would be the best of many choices.
Do you have snakes there? Sometimes even harmless snakes can cause problems.
Does she ever become weird when she doesn't feel 100%, or is this completely out of character?
Please keep us posted. Prayers for her to be healed and well enough to not even need an appt. with the vet, and for you as you wait, which is the most difficult part sometimes. (((Hug!)))
Oh, and please don't give me anymore gray hairs if you can help it!
Love All Life, Thank You For Posting! :)