(sorry for my grammar if I make any mistakes, English is not my mother tongue)
I am an owner of a 6 year old 20 kg (44 pounds) dog. I would always describe him as the most energetic and playful dog ever. However, his behavior changed immediately about two weeks ago.
He hurt his paw, but not on the sole. He could walk normally, and the wound is healed now, even though the healing process took a little bit too long (there were no signs of infection, no swelling whatsoever).
From the day he hurt his paw, he has been behaving in a very unusual way for him. He does not want to play anymore (does not even care about his favourite ball or my dad tickling him), he does not run anymore and his body posture looks as if he was saying "I'm sad and tired of life". He doesn't really wag his tail, his ears do not lift and he and does not get excited before walks (usually he would make a huge mess running in every direction possible, jumping and happy-howling), he just goes near the front door and waits. Same with food.
He is also kind of scared of us. When we call him, he just walks away and hides behind furniture. (Maybe he is scared that we'll try to disinfect his paw again. We used octenisept though, this does not hurt).
Also, he's scared of being outside and that's really weird since he used to spend most of his time in our yard. When we let him out, he keeps scratching the door and jumping on the door handle. If he manages to sneak into our house, he cannot be taken outside without using force (he used to hate being inside).
What makes me worried the most is that from the time it all started, he starts to get overheated very easly. We first noticed it after my mum brought him home after a 2 hour long walk. He could cool down in a lake during the walk. When he got home, he just laid himself on the floor and started breathing very fast (no panting though). I tried my best to cool him down (I placed bottles with cool water near him and turned a fan on) and he got back to normal state after two hours. He did not have any problems walking, breathing ect, he was just very hot. And it was just 21*C (69*Farrenheit) that day. Right now, he gets overheated even faster, but recovers faster too.
His gums look ok, there are no signs of ilness on his skin/fur.
Is it something serious? Will he recover from it? Or is he just getting old?