Lethargy means late response to the external stimuli. This is general sign of illness in dogs. If lethargy continues for more than 24 hours then get advice from vet by taking your dog to him. Following are some common reasons of lethargy in dogs.
1. Electrolyte imbalance
2. Anemia
3. Cardiovascular disorders
4. Infections
5. Hormonal disorders
6. Cancer
7. Skin diseases
8. Eye diseases
9. Toxic reactions
10. Side effects of medicines
11. Immune diseases
So, take your dog to vet for diagnosis and treatment.
1. Electrolyte imbalance
2. Anemia
3. Cardiovascular disorders
4. Infections
5. Hormonal disorders
6. Cancer
7. Skin diseases
8. Eye diseases
9. Toxic reactions
10. Side effects of medicines
11. Immune diseases
So, take your dog to vet for diagnosis and treatment.