My dog has been acting strange lately — should I be worried?

Hi everyone, I have a dog named Bori, and recently I noticed some changes in his behavior. He seems a little quieter than usual and sometimes just sits and stares instead of playing like he normally does. He still eats, but not as excitedly as before. I’m not sure if this is something normal for dogs or if I should be concerned. Has anyone experienced something similar with their dog? I would really appreciate any advice or things I should watch out for. Thank you! 🐶