My 3-year-old dog used to be energetic. Why is he so tired now?

At 3years of age he would generally expected to be more active but every dogs character is different and some are very placid. If his behavior has changed over the last 3 months I strongly recommend a full health check by your vet to rule out medical or painful conditions which may be reducing his mobility

This sudden change in behavior is quite concerning that Fudge is not feeling well. I'm concerned that something serious may be going on. I would have him seen by a veterinarian as soon as possible for an exam and bloodwork.

This can be caused by many different things, including impending illness, stress, pain, a change in his environment, behavioral, etc. I would recommend a good checkup with a vet to see if there is a medical cause. The vet will perform a thorough physical exam and look for any abnormalities or sources of potential pain. Bloodwork may be recommended to for internal medical illnesses. If nothing is uncovered, then they may discuss other treatments such as things for stress or help you evaluate what started this new attitude.

It sounds like Marco may be in pain. Being in pain would lead him to be less active that usual (lethargy) and appear uncomfortable. I'd take him into the vet first thing in the morning. If he is in pain, the vet can diagnose the cause and can give him pain medication. Please do not give him any human pain medication, as many are toxic to dogs and can be fatal if given. Best of luck.

Given that this is a change to his behavior a quick check up to rule out underlying medical causes such as heart disease or early arthritis would be recommended. If all clear then limiting the exercise to 50-60% of the current time and reducing the intensity by throwing them less far should keep him interested and excited without tiring him completely

Thanks for using Petco Pet Education Center, formerly Petcoach! Lack of energy can be the sign of many things that go from just being tired to actually representing a problem like due to pain for example. If he is otherwise fine, I recommend you keep a close eye on him for now. If there is no improvement within the next 2-3 days, have him evaluated by a veterinarian for further assessment and treatment. Good luck and have a great day!

Yes, it could be Willow isn't feeling well. Lethargy is a very general sign of illness, so keep an eye on him for now. If this behavior continues over the next 24 hours, or he develops other signs such as anorexia, vomiting, or diarrhea, take him into a vet right away. Best of luck, I hope this helps!