[Help] My Mom is leaving and her dog is not well. I think he should go to the vet.

Ziggy is approx 4 y/o, unknown breed (perhaps Jack Russell Terrier?), adopted as a pup from the Humane Society of Southern Arizona.Here is Ziggy as of this very moment.My Mom took her dogs on their morning walk yesterday, as she does every weekday, and she noticed that Ziggy slowed down near the end of their walk. This is unusual for Ziggy as he usually leads but she didn't think anything​ about it. Ziggy went potty on their walk and she said nothing was unusual when she picked up his stool.Fast forward to mid-day when I came over to visit. 2 of the 3 dogs greeted me at the door, but I heard a strong cry come from the living room where (I assume) Ziggy must have jumped off the couch like usual, but maybe landed wrong. I watched him jump back on to the couch with ease shortly after this. He lay there either trembling or twitching. I think it was a muscle spasm, but I can't sure. I checked his entire body, rubbed him all over, picked him up, felt his nose, moved all of his paws, legs, tail. He never once winced or cried during my assessment. I had him get up and walk and he had his butt turned down toward the floor and he seemed a little stiff, but not obviously. He slept last night, he seems very tired. He jumped on the couch again, twice actually, without any signs of struggle.My mom is leaving for two days and I'm in charge of watching the dogs. I don't feel comfortable with him like this because he's obviously in pain. My Mom doesn't seem as worried about it, so maybe I'm overreacting. So here I am, asking for your opinions or maybe someone knows what could be the problem. What do I do, fellow dog-loving-Redditors? via /r/dogs http://ift.tt/2qELpfF