It may be normal for a cat's belly to rise and fall quickly while sleeping, but it may also be a sign of certain health problems. Here are some possible causes:

Normal breathing: When a cat is sleeping, his breathing may be slower than Slightly faster when awake, which may cause the rise and fall of your tummy to appear more noticeable. This is usually normal, especially during deep sleep or dreaming.

Heat dissipation: Cats have some sweat glands on their abdomen, which can help regulate body temperature by dissipating heat through breathing. When a cat feels hot, the rise and fall of the belly may increase.

Dreams: Cats may dream while sleeping, and activities in the dream may cause breathing to increase and the stomach to rise and fall.

Health problems: Certain health problems, such as respiratory infections, heart problems, or lung problems, can cause your cat to breathe abnormally while sleeping. If your cat is also experiencing other unusual symptoms, such as coughing, difficulty breathing, shortness of breath, or unusual breathing sounds, you may be concerned and consider consulting a veterinarian.