Cat Suddenly Lethargic and Weak: Reasons Why & What to Do

Cats love sleeping and spend many hours of the day lounging in their favorite spot.

This can make it somewhat difficult to notice lethargy in cats. However, if your cat is suddenly lethargic and weak, ignoring things they usually love and lacking in overall energy, this is a sign your cat isn’t feeling well.

Lethargy and weakness are linked with many medical conditions. When cats are sick it is normal for their behavior to change. Their energy is going towards recovery and so they lack energy to spend on doing the things that they love!

In this article, I look at the possible reasons why you might see your cat acting lethargic. These issues range from minor problems to more severe medical conditions that need urgent attention from your vet. If there is something drastically wrong with your cat, you should notice other symptoms manifesting alongside lethargy and weakness.

Therefore, I also discuss some of the symptoms you might see and when you need to visit a vet. It’s not nice worrying about your kitty but keep reading for all you need to know. You’ll have peace of mind, plus you’ll be able to get your cat the care it needs if necessary.

What Is Lethargy?

I’m going to start by talking a little about what lethargy is and its symptoms. Many people assume that lethargy simply means sleeping all the time. However, as we all already know, cats love sleeping all the time as it is! But lethargy is different.

What lethargy really refers to is an overall weakness and lack of energy. Your cat will lack interest in activities it usually loves, such as playing with its toys or getting excited about food. They will not be as responsive as their surroundings and, yes, they will sleep even more than usual. Therefore, the symptom of lethargy is usually characterized by:

• General tiredness and drowsiness
• Lack of energy and weakness
• Unresponsive to or disinterested in their surroundings
• Increased inactivity

Lethargy can sometimes occur and be nothing to worry about. For example, elderly cats at usually much more lethargic and weak than playful kittens. This is a natural part of aging and is nothing to be too concerned about, especially if there are no other symptoms.

However, if you see your cat suddenly acting lethargic and weak, it is almost always a sign that something isn’t quite right. Taking time to rest is your cat’s way of helping them recover from whatever illness or condition they are suffering from. They can put all their energy into getting better quickly and it is a natural response to feeling unwell.

Moreover, you’ll likely notice other symptoms in combination with lethargy if your cat is sick. This will depend on the precise problem they are facing, but some of the common and more generalized symptoms of sickness you might notice include:

• Increased Affection: Are you wondering why your cat is so affectionate all of a sudden? Some cats seek reassurance from their owners when they are unwell, meaning clinginess and lethargy often go hand in hand.
• Hiding Behaviors: Whereas some cats seek reassurance, most will retreat and hide when they are ill or in pain. So, if your lethargic cat is hiding and acting weird, this is a good indication that something is wrong.
• Weight Loss of Gain: Many illnesses will alter your cat’s appetite and/or activity levels. They may also affect their metabolic rate or blood sugar levels. Therefore, unexpected weight changes – either a loss or gain – are common in lethargic cats that are unwell.
• Dull Coat or Hair Loss: The pain and discomfort that accompanies sickness can cause cats to feel stressed and anxious. In many cases, this manifests as excessive self-grooming which leads to hair loss. Moreover, an unkempt coat echoes the issues going on inside the body.
• Sleeping Positions: Sick cats will often sleep in strange positions that relieve pain and pressure from the area of discomfort. It is important to know all the cat sleeping positions when sick so you can catch any signs of illness early on.

Why Is My Cat Suddenly Lethargic and Weak?

If you have noticed your cat is acting lethargic all of a sudden and potentially shows some of the accompanying symptoms above, something likely is wrong with them. However, you must know precisely what is wrong with your cat so that you can help them get better.

Lethargy is a symptom of a huge range of medical conditions; some are minor and need little to no help from you, whereas others are serious and potentially life-threatening.

As such, I have split this section into three: (1) common minor problems; (2) common serious conditions; and (3) rarer serious conditions.

1. Common Minor Problems

In many cases, lethargy is a symptom of a more minor condition that is unlikely to be life-threatening or cause any long-term harm to your cat. Usually, this will be in combination with other symptoms of the disease. Here is a quick look at some of the most likely explanations and their usual clinical signs:

• Intestinal Parasitic Infection: Worms are parasites that can infect your cat’s intestines and cause them to become lethargic. They are extremely common in kittens as they can be contracted from the milk of their mother. In fact, sudden lethargy in kittens is most commonly the result of a worm infection. If your cat is not eating much but seems fine, it may have worms. Other symptoms include vomiting, diarrhea, and worms in their stools.
• Arthritis: Arthritis is a degenerative joint disease that frequently occurs in senior or overweight cats. It makes the movement extremely painful, which can discourage a cat from moving and cause an increase in lethargic behavior. If you notice your cat struggling to get up, walking stiffly, or having swollen joints, arthritis is a likely cause.
• Respiratory Infection: Common respiratory infections can cause sudden lethargy and weakness in cats. This is where viruses or bacteria infect the upper respiratory tract similar to the human cold. If you see a cat breathing heavily while resting, sneezing and coughing, or with discharge from its nose, this can all be signs of an infection. As your cat fights off the cold, they will be weak and tired.

2. Common Serious Conditions

Lethargy is also a symptom of several common yet more serious conditions in cats. These medical conditions have the potential to cause more long-term damage. If you think any of the below are applicable, you need to book an appointment with your vet right away:

• Diabetes: Diabetes is where your cat cannot control its blood sugar levels effectively. The lack of energy being effectively taken from the diet causes lethargy and weakness. It also leads to increased thirst and urination. More common in senior felines, an older cat not eating is another common sign. However, despite the increase in appetite, diabetes often leads to weight loss. My cat is so skinny and she has diabetes!
• Viral Infections: More serious viral infections such as feline immunodeficiency virus (FIV) or feline leukemia virus (FeLV) lead to severe lethargy and weakness. Both of these are serious conditions. Most vets agree that cats with FeLV should be put down, whereas cats with FIV usually have a life expectancy of five years from diagnosis.
• Abscesses: An abscess is an infected bulge that is filled with bacteria and pus that can visibly be seen under the skin. They are the body’s natural response to infection, often developing from a bite wound in a catfight. The abscess will need to be drained and your cat will be prescribed antibiotics to treat the infection.
• Heartworm: Heartworm is a specific type of parasitic worm infection more serious than those mentioned above as these worms can grow up to a foot long. Aside from lethargy and weakness, common clinical signs include vomiting and diarrhea, breathing difficulties, coughing and gagging, and weight loss.
• Anemia: Anemia is where your cat is lacking red blood cells and so struggles to carry enough oxygen around the body to where it is needed. This means their muscles tire more easily, causing a cat to be suddenly lethargic and weak. You can also check for pale gums, the most easily observed clinical sign of anemia in cats.
• Urinary Tract Infections (UTIs): Lethargy and fatigue are not immediately thought of as a symptom of a UTI, but such behavioral changes are commonly seen. If your cat keeps going to the litter box but nothing happens, they may have a UTI. Also watch for your cat urinating outside the litter box, urinating frequently, or signs of blood in their urine.

3. Rarer Serious Conditions

If your cat is weak and lethargic, one of the conditions I have already mentioned is more likely than not to apply. However, there are some less common yet severe conditions you should also be aware of as they require prompt medical attention. Here is a quick look and their related disease-specific symptoms:

• Poisoning: Cats love to explore and can easily get their curious paws on a toxic substance. If they ingest this, they can poison themselves. The severity of the poisoning depends on what substance and how much of it they consumed. However, the substance will typically cause lethargy and weakness, vomiting and diarrhea, difficulty breathing, and even seizures.
• Heatstroke: When cats get too hot and cannot cool themselves down they may go into heatstroke. This is where their bodies become severely overheated, causing their heart rate and respiratory rate to increase to dangerously high levels. You will likely notice drooling and salivation in an attempt to cool down, along with vomiting, dizziness, and staggering.
• Heart Disease: Heart disease is a progressive condition that usually goes unnoticed in the early stages. However, as the condition worsens, your cat will start to become more lethargic as the heart struggles to pump enough blood and oxygen around the body. There are few other signs to look out for other than loss of appetite and weight loss, which is why it is known as the “silent killer”.
• Organ Failure: When an organ such as the kidney or liver goes into failure this causes weakness and lethargy. In both cases, early treatment is critical. Liver and kidney failure too have similar clinical signs, including loss of appetite, vomiting, and weight loss. Additionally, cats will liver disease may develop jaundice or abdominal swelling.

What Should I Do if My Cat Is Acting Lethargic and Weak?

Your first point of call should always be to speak to your vet. They will be able to offer a formal diagnosis and treatment if anything is wrong.

For cats that are showing no other symptoms, don’t speak to your vet prematurely. Occasionally, lethargy can come about due to overeating or something minor like a hairball. These are no real cause for concern and will correct themselves within a few hours. Instead, wait for 24 hours and if your cat is still weak and lethargic, then call your veterinarian.

On the other hand, if your cat is showing other symptoms alongside lethargy, don’t hesitate to call your vet immediately. Some of the more serious causes such as poisoning need prompt treatment. Leaving your cat 24 hours to see if they get better could end up costing them their life.

MY FINAL THOUGHTS

Lethargy is a symptom of many medical conditions, ranging from a mild respiratory infection to something more life-threatening like poisoning, liver failure, or heart disease.

In most cases, whenever something is wrong with your cat other symptoms will also manifest. For example, if your cat is lethargic and not eating, acting overly affectionate or aggressive, or is losing or gaining weight, they are probably ill. Other disease-specific symptoms could also present themselves.

If in doubt, always call your vet. Keep an eye out for other symptoms as this can help the vet with a diagnosis. Depending on the diagnosis, your vet will recommend treatment or another course of action that is best for your furry friend.