My dog is shaking after his visit to the groomers?

We went to the Petsmart to get my purebred shih tzu shaved, now my dog kind of looks like a rat (he had mats so we had no choice), but one weird thing I noticed is that he's extremely fidgety and shaking a lot. It's like when a person gets the chills, but my dog can't even take a normal nap without shaking his ears, jumping, or shivering. I'm really worried because he's only a year and 7 months old. Thanks for the help :/