My Chihuahua from home used to get like that sometimes. We emergency rushed her to the vet on the first occasion that it happened and they found nothing wrong with her. $300 for nothing, but we were glad she was okay. It's happened several times since then. I noticed if she was ever constipated, she acted that way towards me. I think that could have been the issue the first time. She also rough-houses with the cat sometimes, then afterwards she can act that way. Maybe she gets popped by the cat and doesn't feel so well after. So it could just be a matter of being in minor discomfort or pain.
But if your Chihuahua starts exhibiting any serious signs such as diarrhea, vomiting, no interest in food, not willing to walk, etc... I would definitely take her to the vet. Or if she keeps acting this way for more than a day. My Chihuahua was always back to herself in no more than a day if she was acting like that.