Cat person? How many pictures of your cat sleeping do you have on your phone? A lot, right? They are so cute when they sleep…so cute. But then they are always asleep. Okay, not always, but a lot of the time. Why is that?

The truth is that cats sleep an average of 15 hours per day. Some of them stretch that toward 20 hours, especially older cats and kittens. Old age and the folly of youth, that’s understandable; they take their toll. What’s wearing out the rest of them?

Cats are natural predators. Their prey is quick and elusive. Sneaking up and pouncing—repeatedly—is undoubtedly exhausting. Cats in the wild work hard in order to meet their dietary needs, and expending that kind of physical effort requires a lot of recharging.

And they are not just predators, they are crepuscular predators, which means that the go lights come on for them at dawn and dusk during the twilight hours when their prey—rodents and birds—are equally active. The rest of the day, cats sleep, though that sleep is of two types.

About three-fourths of their sleep is a shallow, almost-waking rest called slow-wave sleep (SWS). Cats doze in a kind of ready position, their senses of smell and hearing in the “on” mode. Ears occasionally twitch. Peaceful but poised, they are ready to react instantly: to pounce on prey or to swat and scratch the hell out of you for the temerity of petting them while they are sleeping. These famous catnaps usually last 15–30 minutes.

The other one-fourth of the time, cats really are out of it, sleeping deeply, often reaching REM sleep. If it looks like they are dreaming when their paws tremble, it is because they probably are dreaming. This deep sleep usually comes in five-minute increments that are broken up by dozing.

So what about my domestic, never-leaves-the-house cat? She who stalks her meal by sidling up to a bowl. Why is she always sleeping? In a word: heredity. As a species, cats—whether they sleep on the street or cuddle on a sofa—are all hardwired to the same internal clock, and it generally has the snooze button depressed. That, and house cats also sleep when they are bored.

By Jeff Wallenfeldt Courtesy Britanica