Behavior Changes
A first step in diagnosing a dog health problem is to look at your dog's behavior. If your dog generally doesn't whine or cry much, and yet today seems to be complaining a lot, something is probably wrong. If your dog is crying, tensing up and crouching, he may be experiencing pain, usually abdominal. This could be due to bloat or ingesting poison or a sharp object. A dog may have an object stuck in the mouth or throat if he is choking, drooling, gagging or pawing at the mouth. Convulsions or thrashing about with rigid movements, glassy eyes, or a foaming mouth usually indicate acute distress either from poisoning, possible epilepsy or extremely low blood sugar.
Energy Changes
Take note if a dog has a sudden decrease in energy and seems lethargic or disinterested in a favorite toy or activity. If the lethargy persists for several hours despite a nap, your dog may be ill. Low energy can mean that an infection, such as a skin infection, has become systemic. In the summer months, sudden exhaustion can indicate heat stroke or dehydration. A suddenly inactive dog may be experiencing a sudden onset of depression due to pneumonia, fever, a severe allergic reaction or problems with the heart.
Elimination Changes
Noticing changes around your dog's patterns of peeing and pooping is another first step in diagnosing a problem. A dog may have a urinary tract infection if he suddenly starts peeing in the house or resists going out to pee. If a dog is scooting on the floor on his rear end or hiding under a bush, he may be constipated or have blocked anal glands and feces stuck in the hair around the rectum. A dog with a kidney or bladder infection may squat numerous times without being able to produce a normal amount of urine, if any. Any straining around elimination indicates a possible infection or blockage.
Physical Changes
Many seemingly minor physical changes can be an indication of a dog health problem. While you can't run to the vet every time your dog's body has a slight change, you can get an idea of his general health by looking at a cluster of changes. A healthy dog's nose and mouth are wet. Sometimes a dog's nose is dry after sleeping but if both the mouth and nose are dry, it can be a sign of distress related to heat stroke or general illness. Any sort of panting or rapid breathing is also a sign of distress. This can indicate pain, pneumonia, heat stroke, an obstructed airway, heart problems, or poisoning. If a dog faints, heart disease is also indicated. Bad breath, beyond what results from infrequent tooth brushing, may indicate many varieties of worms, rabies or other infections.