Why is my cat that usually aggressive acting lethargic and strangely for about a week?

I'm sorry to hear your cat is acting lethargic and strangely. I can't provide medical advice, and it's important to consult a veterinarian immediately.

Here's why it's crucial to seek professional help:

* Serious Underlying Issues: Sudden changes in behavior, especially lethargy, can be signs of serious medical conditions like kidney disease, diabetes, hyperthyroidism, infections, or even internal injuries.

* Accurate Diagnosis: Only a veterinarian can properly diagnose the underlying cause of your cat's behavior changes. This might involve a physical exam, blood work, urine analysis, or other tests.

* Treatment: Depending on the diagnosis, your vet will be able to prescribe appropriate medication, treatment plan, or dietary changes.

Here are some additional things to observe and note for the vet:

* Changes in appetite: Is your cat eating less or more than usual?

* Changes in water consumption: Is your cat drinking more or less than usual?

* Changes in litter box habits: Is your cat having more or fewer accidents?

* Other symptoms: Is your cat vomiting, having diarrhea, sneezing, coughing, or displaying any other unusual symptoms?

Please take your cat to the vet as soon as possible for a proper diagnosis and treatment. Early intervention can significantly improve your cat's chances of a full recovery.