Chinchilla not as active

Hey everyone, I’ve been noticing for the past week that my chinchilla Gizmo isn’t as active as he normally is. He doesn’t appear to have any major issues going on, he’s eating and drinking normally, poops normal size, still very alert and affectionate. However, he’s not jumping on his high ledges anymore and running on his saucer much less. I’m not sure how old he is exactly as I rescued him, but I have had him for about 11 years. He doesn’t appear to be injured in any way, which was my first concern, but he doesn’t seem to have any problems physically. Does anyone have any idea what might be going on? Thanks everyone!