My dog has been acting fine all day, but is now starting to act strange.

My dog has been acting fine all day, but is now starting to act strange. She is suddenly very lethargic, shaky, and jumpy. I have checked her out the best I can and have also found that her stomach is tight, there is a faint paleness to her gums(but they change color quickly), no panting, no loss of appetite or water intake, gagging a few minutes ago, still responds to calls(tail wagging, ears raising, moving around), and no sore spots.
I have looked on websites but there is no match. Does anyone know what is or could be wrong?

do you looked for scabies my dog had the same.
let your pet doctor scrath deep !