Sick Chihuahua

I have a seven-year-old female Chihuahua, and we've taken her to the vet three times, and have yet to find an answer or medicine to take care of what's wrong with her. We have been experiencing events where she acts completely different. She runs around in circles. Seems like she doesn't know where she's at. She lifts her foot up and down, up and down, up and down, moves her head all around, all around, won't eat, whines, doesn't act like her personality at all. It will last for a day to a day and a half, and then she just comes out of it, and she's back to normal again. And then it could last clean for a day, maybe two, three, and then all of a sudden she does it again. There's nothing that triggers her. While she's in this fit, she whines and whines, runs around in circles again, repeats all the same behaviors, and then just comes out of it. A couple days later, or it could even be one day, she does it again. It's been an ongoing event that we don't know how to handle it. We've taken her to three vets. Nobody's been able to diagnose it yet. Please, please help us. Anybody that has had a dog that has acted like this. please get ahold of us