For dogs that are not yet adults, it is generally considered to be caused by viral infectious diseases caused by parvovirus and canine coronavirus infection, or it may also be caused by diseases such as bacterial gastroenteritis.

For adult dogs that have been vaccinated on time, in most cases, it is considered to be caused by diseases in the uterus, kidneys, liver, etc., or it may also be caused by poisoning and other reasons.

Because it is more difficult for dogs to regulate their body temperature than humans, they may suddenly become lethargic due to changes in temperature. Because the body temperature of dogs is higher than that of humans, and their bodies are covered with fluffy fur. Especially on days with high temperatures, many dogs suddenly collapse.

Dogs, like people, feel very depressed for some reason. When the owner scolds the dog and cannot take it for a walk, and when the dog is in a low mood, it is easy for the dog to become lethargic, especially when there are many days when the dog is in a low mood without any reason.