
Sounds like what we call a TIA or mini stroke in humans, can last a few minutes or a few hours and suddenly reverts back to normal when what ever was causing the blockage of the blood supply clears.
I would take her to the vet and get her checked out, a friend of mines old cocker had mini strokes and was treated with a daily childs aspirin and they stopped and one night 3yrs later she died peacefully in her sleep in bed with her owner.