If you notice your dog acting listless during the day, you might assume it's laziness. If this is uncharacteristic for your pet, you might need to wonder if he's dehydrated or maybe it's heat stroke.
If your friendly and gentle natured dog is exhibiting signs of aggression toward anyone who comes near him, you have to wonder if he's in pain, perhaps a bad tooth? You have to learn to read signs that aren't vocalized. Most importantly you'll need to be an advocate of your dog because if you aren't, who is? You took on his wellness when you invited him to join your family.
Finally, in all my experiences with dogs, this one has been the hardest to identify. A regression in house breaking. Your dog has been house broken for months or years and suddenly he's having accidents in the house. Or maybe he hasn't lost complete control, but you've noticed his need to go outside has increased. It's up to you to determine whether there is a bladder/urinary tract infection or if it's behavioral. And more difficult to identify yet, is when it started as a physiological problem then it became behavioral.
With our lab puppy, he had UTI's for the first 2 months that we had him. It went undiagnosed because he wasn't housebroken yet and there was a very fuzzy line between a puppy who was in training and "Is it just me or is he peeing at an unusually frequent rate?" Through our battle with this, we learned that frequent "sensations" to pee, but little output is a good indicator that there's an infection brewing. If you are noticing this, you can simply collect a tiny urine sample (just sneak a clean bowl under him/her mid stream, then suck it up in a syringe or pour it into a zippered baggie) then take it into your vet for a quick urine analysis. They can tell you in a matter of minutes if there's a presence of blood or white blood cells. Antibiotics are prescribed and the infection should clear up with a few days.
Now for the tricky part. Once your dog is cleared from having an infection (or perhaps they never had one), now you're left dealing with the behavioral aftermath. There's a chance that your dog might need a refresher in house breaking. If you have a strong-willed dog like we were