If your cat suddenly becomes aggressive, it’s important to take it seriously and take steps to address the behavior. Here are a few things you can do:

1. Consult your veterinarian: Your cat’s aggression could be a symptom of an underlying medical condition, such as pain or a thyroid problem. Your vet can help rule out any potential medical causes for the behavior.
2. Identify the trigger: Try to identify what is causing your cat to become aggressive. Are there certain times of day when the behavior occurs? Are there certain people or animals that seem to trigger it? Understanding the trigger can help you take steps to avoid or manage it.
3. Modify the environment: Remove triggers, if possible, by removing certain objects or keeping certain animals away, especially if they are consistent with the aggressive behavior
4. Provide positive reinforcement: Reward your cat for calm, non-aggressive behavior with treats, toys, and affection.
5. Provide an escape route: Aggression can often be the result of a feeling of being trapped or cornered. Making sure your cat has a way to escape from a situation before it becomes aggressive can help prevent aggressive behavior.
6. Seek professional help: If your cat’s aggressive behavior continues despite your best efforts, consider seeking the help of a professional animal behaviorist or a veterinary behaviorist to help you address the behavior.

It is important to keep in mind that aggressive behavior can be dangerous for both you and your cat, so it is important to address it as soon as possible.