What this means
Sudden weakness looks like this: the dog was walking or running normally, then suddenly stops, props itself up, its hind legs begin to give way, it staggers, lies down or even collapses. Sometimes the episode lasts only a moment and the dog looks normal again, so an owner may think it was "just tired".
This is not ordinary tiredness. Sudden weakness can mean that the heart is not beating evenly, that the brain is short of sugar or oxygen, or that there is some other general problem. Which of these is the real cause can only be found by a vet who examines the dog and runs tests. Even if your dog seems perfectly well after the episode, it is still worth having it examined.
Write down what your dog was doing before the episode: running, playing, excited or a long time without food, and how long the weakness lasted. Notice the colour of the gums and the breathing if you can do so safely. If possible, film a repeat episode. These notes help a vet more than a general "sometimes goes limp".
Possible causes
These are things that can cause this sign. It is not a diagnosis, and they are not equally likely for your dog.
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A heart rhythm problem
When the heart beats unevenly, blood may sometimes not reach the brain and muscles well enough. The dog may suddenly weaken, especially when running or excited.
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Low blood sugar
When there is too little sugar in the blood, a dog can suddenly become weak, wobble or be unable to stand. It is seen more in small puppies and in dogs that went long without food.
About the condition: Hypoglycemia (low blood sugar) -
Blood loss or anaemia
When there is too little blood or too few red cells, muscles get less oxygen. The gums may look pale.
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A breathing or lung problem
If a dog is not getting enough oxygen it can suddenly weaken. A change in breathing is usually seen alongside.
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Overheating
On a hot day or after heavy exertion a dog can suddenly become exhausted and collapse. This is a dangerous condition.
About the condition: Overheating (heat stroke) -
A nerve or muscle problem
Some nerve and muscle problems cause sudden giving way of the legs or collapse. A vet has to work out where the problem lies.
What else to watch for
These observations help your vet build the picture faster. Note down what you saw and when.
- What your dog was doing before the episode: running, playing, excited or a long time without food
- How long the weakness lasted and how quickly your dog recovered
- The colour of the gums during the episode: pale, bluish or normal
- Whether breathing changed or your dog coughed
- Whether episodes repeat and how often
- Whether your dog lost consciousness, trembled or staggered
When to book a routine visit
Even if your dog recovered after sudden weakness, book a vet visit soon rather than waiting to see whether it happens again. Say what your dog was doing before the episode and show any video you have.
Related conditions
Conditions whose entries mention this sign. The list is somewhere to read on, not a way to reach a diagnosis.
- Arrhythmogenic right ventricular cardiomyopathy (ARVC) Heart This is an inherited disease of the heart muscle in which the muscle cells of the right ventricle are gradually replaced by fatty and fibrous tissue. This disturbs the heart's electrical signals and causes rhythm disturbances that can lead to weakness, fainting or even sudden death. The disease can go a long time without any noticeable signs, so the heart rhythm needs to be assessed by a vet.
- Hypoglycemia (low blood sugar) Hormones and metabolism Hypoglycemia is a condition in which the level of glucose in the blood drops too low and the brain and muscles run short of energy. It can affect young puppies and small dogs, especially if they have gone a long time without food or are exhausted, as well as dogs with certain diseases. Hypoglycemia can quickly become life-threatening, so the dog needs a vet immediately.
Body systems: Heart Hormones and metabolism