If your dog’s onset of lethargy is very sudden and they collapse, this indicates an emergency and they should be seen by a veterinarian immediately.
A sudden collapse can indicate internal bleeding, a seizure, or a syncopal heart episode; all of which require immediate medical attention.
If their lethargy presents more as slow laziness, it’s okay to monitor for 24 hours to see if they improve with rest.
It’s important to note if your dog’s lethargy is accompanied by any other clinical signs, such as loss of appetite, obvious pain, fever, vomiting or diarrhea, breathing difficulties, behavioral issues, trembling, or disorientation.
Taking a mental note of all of your dog’s symptoms will help you and your veterinarian determine how serious the problem is.
Pro Tip:
While general tiredness without any other symptoms can usually be monitored for improvement after some rest, any other symptoms such as not eating, pain, vomiting or diarrhea are all signs of an urgent underlying issue.