Cats are mysterious creatures and display a myriad of bizarre behavior. All of them are driven by their instincts. Sleeping too much is also one of such instinctual habits, and seasoned feline parents are accustomed to this habit.
However, all novice cat parents who first adopt a cat in life get disturbed and worried when they notice their cat is always sleeping.
Before jumping to the reasons “why do cats sleep so much,” We would like to clarify that cats have evolved to sleep 12-15 hours daily. Even kittens or older cats may sleep up to twenty hours. Wild cats also take a long sleep daily, so most of the time, nothing to bother if you observe your cat taking a nap for several hours continuously.
Let’s briefly discuss the reasons why cats sleep so much.
Natural Predators / Energy conservation
Cats are carnivores and predator animals by nature. All carnivore animals (including lions, tigers, etc.) spend most of their time resting or sleeping when they are not hunting. These animals struggle to track their food in the wild because their prey is usually sharp, elusive, and challenging to catch. So it requires a lot of physical effort to ambush for several minutes and swoop swiftly on the prey repeatedly.
So to get rid of the fatigue of the previous hunt and to conserve and replenish their energy reserves for the next hunt, they spend most of their time resting or sleeping.
Although our domestic cats get ready-made food and don’t hunt, the instinct to sleep and get ready for the hunt persists.

Crepuscular By Nature
Stating cats as predators is not enough. To be more precise, cats are crepuscular predators. In the animal world, the word crepuscular is used for those animals that are more active during the low light hours (at dawn and dusk).
The evolution of such instinct may be because their primary preys (like rodents and birds) are also active at these times of the day. So as a predator, they will not have to search for long to find their prey.
Although most domestic cats follow human sleeping patterns, many examples are available when cats persist with their wild instinct regarding sleeping habits. So your cat may have a complaint against you that you sleep most of the time when he is awake.

Your Cat Is Not Sleeping Actually
Most of the time, when you consider that your feline friend is sleeping, he may not be sleeping actually. During 75% of their sleep time, cats snooze, which means their eyes are closed, but their senses of smell and hearing are functional, and they will respond instantly to any external stimuli.
The condition is called waking rest, during which they are not sleeping, but they still get necessary recharge.
For the rest of the 25% duration, they sleep in the real sense, and the state is called deep sleep.

Old Age
As the cats grow old, their energy level also decreases. So they become less active, and their sleeping time increases too.
Research has shown that once cats are 11 years old, their sleeping time increases yearly. So if you own a senior cat, you can expect 15 -20 hours of sleep.
Stress & Boredom
Another possible but less common reason for your cat sleeping more is that he may be bored, stressed, or afraid. When cats have nothing to do, sleeping is the only option to spend time. In addition, hiding or being less active is a catty way to overcome stress or fear.

Medical Reasons (Sick or Uncomfortable)
A sudden increase in the sleeping time of your cat than usual may be due to medical reasons. So if you know your cat’s routine and observe a sudden rise in his sleeping time, you should look for reasons other than those stated above.
Some possible reasons include obesity, rapid weight loss, hiding, lethargy, endocrine diseases, arthritis, heartworm, diabetes, etc.
Conclusion
Sleeping is the cat’s instinct. All carnivore animals sleep more than other animals because hunting requires much more physical effort than grazing.
It’s a tiring job, so they sleep to conserve their energy for the next hunt. For cats, 12-15 hours of sleep is normal; even kittens or older cats may sleep for 20 hours. However, if there is a sudden increase in the sleeping time, you should seek medical reasons and a vet’s help.