Inside dog health problems?

We have two Golden Retrievers. Sammy, 5 and Misty, 4. We'd had Sammy as an inside dog ever since we got him (six weeks). As of maybe yesterday we noticed he doesn't seem to be as normal as he's been. Yesterday my sister and I encouraged him to hop up on the couch. He got his front end up but then he just laid on the couch with his back end hanging off for a few seconds. When he got his back end up he let out a little whine. He's never done this before. It seems difficult for him to get up from a laying position, and he doesn't seem isn't that excited to eat. Sammy is normally really excited and jumping all over my dad in the morning, but this morning he just kept laying down wherever he had been. I was just curious if the amount of health risks increase or decrease when a dog live inside or outside, or if it is just apart of being a Golden. If anybody could help out with possible conclusion that would be awesome. We're probably going to take him to the vet in a few days if this continues. Thank you soo much everybody.