Folding Dog

My dog was outside and when he crossed the threshold to come back inside his back arched really high, he started shaking, and his legs were folded up and we're almost paralyzed looking (he could not walk). His upper body was normal and so was his face and expression. The vet thinks he possibly had a seizure but my dog was coherent while exhibiting these symptoms and he wasn't drooling or unresponsive. The shaking/paralyzed legs only lasted around two minutes and then he was back to his normal, playful self. Has this happened to anyone else's pet before? Thank you for your help!