If your cat suddenly becomes lethargic and sleeps a lot, it's very likely due to anemia. It may also have pale gums and be thin. It's best to feed it more blood-enriching foods.
A cat's diet shouldn't consist solely of cat food. To supplement their diet, owners need to provide nutritious complementary foods such as chicken liver or duck liver, which can be fed in small amounts once or twice a week. Additionally, meats like fish or beef can be given 3 to 4 times a week. These methods are helpful for cats with anemia, and owners should be consistent in their feeding practices. 
Fruits and vegetables are rich in nutrients and can supplement cats' diets with vitamins and iron, which are beneficial to their health. Therefore, cat owners can feed their cats more fruits and vegetables on a daily basis, such as spinach, apples, and carrots.
If a cat has internal parasites or gastrointestinal discomfort, it may exhibit symptoms such as lethargy, drowsiness, and vomiting. You can deworm it or give it probiotics to regulate its digestive system.
