An abrupt change in a dog’s behavior normally indicates a health problem. Causes may vary, but the most common ones include dehydration; renal and congenital problems, such as kidney disease or diabetes; aging; and pain brought on by physical trauma.
Loss of appetite in a dog usually results from minor changes in his environment, introduction of a new diet or a reaction to vaccination. The owner needn't be alarmed, but if the behavior continues for more than a couple of days, it may indicate serious health problems, such as cancer, dental issues or infection.
Fever, infection or diabetes may explain the dog’s strange behavior if accompanied by excessive thirst; however, the reasons behind the thirst may also include the use of medication that treats seizures and allergies in addition to a sodium-high diet. If the dog changes his social behavior, such as avoiding certain areas of the house and being more aggressive, or if he engages in different sleeping habits, he may be reacting to pain that hinders his normal movement and increases frustration. Another reason for strange behavior is dementia that typically manifests as the dog reaches old age. Dementia can cause the dog to become disoriented and confused, leading to odd behavioral patterns. Stress and conflict in the dog’s environment can lead to the development of a compulsive disorder, which can cause the dog to engage in weird behavior that alleviates the symptoms by reducing the amount of neurotransmitters associated with the stress.