Why Does My Cat... Sleep All Day?- Provided by VetStreet.com
It's no secret that cats are impressive sleepers. In fact, they typically get between 10 to 16 hours of shut-eye each day. That's more than most mammals — except for bats and opossums, who are known to slumber up to 20 hours per day.
Biologists pin this feline affinity for sleep on two things: Their typically protein-rich diet, which requires long periods of rest to aid in proper digestion, and their naturally crepuscular (dawn and dusk) predatory pattern, which means cats tend to hunt twice daily and then rest in between.
Although there’s a lot of individual variation among domesticated felines, indoor cats are more likely to snooze for most of the day, while their free-roaming brethren are more likely to spend their daylight hours stalking small prey.
Bottom line: If your indoor kitty often sleeps the day away, just know that she's a perfectly normal feline. However, if your cat is lethargic — meaning that her energy levels are lower than normal — or she isn't interested in playing or eating, you should make an appointment to see your vet.