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Lethargy and Low Energy

Lethargic dog or cat? Low energy is worth a closer look.

Lethargy means your pet is more tired, quiet, or slow than usual, and it is one of the most common early signs of illness in dogs and cats, from infection and pain to heart, kidney, or hormonal disease. We see lethargic dogs and cats same day, seven days a week.

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Call Us Right Away If

When low energy is an emergency.

A sleepy afternoon after a big hike is normal. Call us right away and come in if your pet's lethargy comes with any of these:

  • ✓Collapse, fainting, or inability to stand
  • ✓Pale, white, gray, or yellow gums
  • ✓A swollen or tight belly
  • ✓Fast or labored breathing
  • ✓Repeated vomiting, or vomiting with diarrhea
  • ✓A cat that hasn't eaten in more than a day, or a dog that has skipped more than a day of meals
  • ✓Signs of pain, such as hiding, trembling, or reluctance to move
  • ✓Possible toxin exposure

Pale gums with weakness and a swollen belly can signal internal bleeding, which is an emergency. Please see our emergency and urgent care page, and if these signs appear after 7:30 PM, go to the nearest 24-hour emergency hospital instead of waiting for us to open.

Common Causes

Sudden vs. gradual lethargy.

How quickly the change happened tells us a lot.

Sudden lethargy, over hours to a day or two, is more often linked to infection, fever, pain, a toxin, nausea, bleeding, heat exposure, or an acute problem like pancreatitis. Mild tiredness for a day after vaccines can be normal, but call us if it lasts longer or comes with swelling or vomiting.

Gradual lethargy, over weeks or months, is often mistaken for normal aging. It can be caused by:

  • ✓Kidney disease or liver disease
  • ✓Heart disease
  • ✓Anemia
  • ✓Hormonal conditions such as hypothyroidism in dogs, hyperthyroidism in cats, and diabetes
  • ✓Arthritis and chronic pain
  • ✓Dental disease
  • ✓Cancer

Cats are especially good at hiding illness, so a cat that sleeps more, stops greeting you, or skips meals deserves a closer look. Cats that go without food for even a few days are at risk of a serious liver condition called hepatic lipidosis. For older pets, regular senior care visits help catch slow changes early.

At Your Visit

Finding the cause at your visit.

Because lethargy is so broad, a careful history is our starting point. Tell us when it began, whether appetite, thirst, or bathroom habits have changed, and anything your pet might have eaten.

We then do a full exam, including temperature, a heart and lung check, gum color, and a feel of the belly. Common next steps include:

  • ✓Bloodwork and urinalysis, with many results in under an hour
  • ✓Blood pressure measurement
  • ✓X-rays of the chest or abdomen
  • ✓Ultrasound of the abdomen or heart, read by a board-certified veterinary radiologist
  • ✓Hormone tests, such as thyroid levels, when indicated

Treatment follows the diagnosis. Some pets go home the same day with medication and a plan, while others need IV fluids and monitoring through pet hospitalization.

We see pets from across the Valley, Santa Clarita, Palmdale, Lancaster, and Ventura, and Santa Clarita families can find directions on our Santa Clarita vet page.

Common Questions

Lethargy and low energy FAQ.

When should I worry about a lethargic dog?
Worry if your dog's low energy lasts more than a day, comes on suddenly, or appears with vomiting, diarrhea, not eating, pale gums, a swollen belly, or trouble breathing. Collapse is always an emergency. Call us for a same-day visit if you are unsure.
Why is my cat so lethargic?
Cats often become lethargic from fever, infection, pain, dental disease, kidney disease, thyroid problems, or diabetes. Because cats hide illness, lethargy may be the only sign you notice. A cat that is lethargic and not eating for more than a day should be seen promptly.
Is it normal for my dog to have low energy as it gets older?
Senior dogs do slow down, but a clear drop in energy is often caused by treatable problems such as arthritis, hypothyroidism, heart disease, or kidney disease. A senior exam with bloodwork can find the cause. Many dogs feel much better once the problem is treated.
Can my pet be tired after vaccines?
Mild tiredness or soreness for about a day after vaccines can be normal. Call us if your pet is very lethargic, the tiredness lasts longer, or you notice facial swelling, hives, vomiting, or trouble breathing, which can signal a reaction.
What tests do you run for a lethargic pet?
We usually start with an exam, bloodwork, and urinalysis, and many results are ready in under an hour. Depending on what we find, we may add X-rays, ultrasound, blood pressure, or hormone tests. The goal is to find the cause quickly so treatment can start.

Is your pet just not acting right?

Trust your instincts. Call us or walk in today, we are open every day from 7:30 AM to 7:30 PM.

Book a visit(818) 922-2209