Lethargy can be caused by a wide variety of conditions, such as heat stroke, hypoglycemia, anemia, pain, or a medical emergency. The list is lengthy, so it’s helpful to take note of any other signs that your dog is showing to assist your veterinarian in the proper diagnosis.
Your dog may need a physical exam and bloodwork to determine the underlying cause and provide the right treatment for them.
Sometimes dogs will recover from a day of lethargy on their own, and sometimes they need to see their veterinarian. Since there are so many possibilities, it’s best to contact your veterinarian if you notice your dog is lethargic and slow.
If your dog becomes lethargic very suddenly and collapses, seek veterinary attention right away.