It might sound bad, but recently I’ve wanted to yell this at my computer a lot.
Your dog’s not jumping a low jump – get a vet check!
Your previously house-trained dog has suddenly started to soil in the house – get a vet check!
Your dog has started performing a new “strange” behaviour, or won’t perform a previously learned behaviour – get a vet check!
Your dog’s gone off his food, doesn’t enjoy her walks, or anything else that’s not normal – your first point of call should always be your veterinarian. Not your friend, not someone on the internet, not Google, but your vet. Book an appointment, or if it’s urgent, call and ask them, all vets will (or certainly should) have someone on-call 24/7 that you can ask a question of.
The one thing you don’t necessarily want to discuss with your vet, is training or behaviour modification – sadly some vets are still in the “dark ages”, and may recommend things such as alpha rolls, harsh ‘nothing in life is free’ programmes, lead jerks, and so on.