8. Hyperthyroidism

This disease is pretty rare among dogs mostly because it is uncommon for their thyroid gland to produce excessive amounts of thyroid hormones. However, in some cases the illness has developed because of a thyroid tumor.

Hyperthyroidism can make  your puppy  lose weight and have an irregular heartbeat. Other symptoms are bark changing, constantly being hungry, aggressive behavior, being hyperactive and so on. If not treated it can get worse.

What can you do? Go to a vet for a proper exam and most likely  he will suggest surgery to eliminate the tumor  after which  they will recover well.