So, today my dog randomly started having trouble jumping up on the bed and couches. Also, he cant run as fast or go up and down stairs as quickly as he did previously... He looks kinda depressed and hasn't smiled

Vets are closed today until tuesday and I gotta spend the next couple days worrying and shit. Has this happened to anyone else's dog? He eats, walks and poops normally too. My dad suspects that he pulled a muscle or injured his back; I'm praying it's nothing too serious.