A British Shorthair that isn't eating, drinking, and only sleeping can be due to several reasons, including catching a cold, experiencing low mood, having gastroenteritis, or contracting feline panleukopenia (also known as feline distemper). It's essential for owners to assess the situation carefully to determine the exact cause.

Possible Reasons for Lethargy and Lack of Appetite in British Shorthairs
Let's explore the common reasons behind these symptoms in your British Shorthair:
1. Common Cold (Upper Respiratory Infection)
If your cat suddenly loses its appetite and sleeps excessively, it might have caught a cold. Alongside lethargy, symptoms such as a dry or runny nose and an abnormal body temperature may be present. You can check your cat's temperature to confirm. If your cat has a cold, provide it with cat-specific cold medicine, and ensure it stays warm.
2. Emotional Distress and Low Mood
A cat's emotional state can significantly impact its appetite and activity level. If your British Shorthair is feeling down, it may show signs of loss of appetite and increased sleep. This can be triggered by a lack of interaction with the owner, feeling neglected, or being suddenly scolded. To improve your cat's mood, spend quality time petting and cuddling it, and try offering some of its favorite treats.
3. Gastroenteritis (Stomach Inflammation)
If your cat's loss of appetite and excessive sleep are accompanied by symptoms such as vomiting and diarrhea, it could indicate acute gastroenteritis. In this case, withhold food for a day, observe the cat's condition, and then administer anti-inflammatory medication followed by probiotics after two hours.
4. Feline Panleukopenia (Feline Distemper)
Feline panleukopenia, also known as feline distemper, can cause loss of appetite and lethargy in cats. This severe viral infection also presents symptoms like diarrhea and high fever. If you suspect your cat has feline panleukopenia, it’s crucial to take it to a veterinarian for immediate examination to avoid delays in treatment.
It’s important to note that these are just potential causes. If your British Shorthair continues to exhibit these symptoms, it is essential to consult a veterinarian for a proper diagnosis and treatment plan. Early intervention can significantly improve your cat's health and well-being.