Is my dog having a seizure !? Please help!?

I have a chihuahua. She is more than 10 years old. She is kind of fat, but I don't know if it has anything to do with this. A few minutes ago my mom saw her fall down and my dog was crying. She couldn't get up and she was twitching. We took her inside and she was twitching and crying even more. She was in a lot of pain and she turned really hot. Finally she calmed down and went back to her normal self. Right now she is really tired and resting, we are going to let her sleep inside just to make sure she's doing better. This is the first time any of us saw this happen to her. Can it happen again? Was she having a seizure? What caused this?