A long day of playing fetch, chasing cars, and going on walks can be exhausting for a dog. But what happens when our four-legged friends catch some shut-eye and how much of it do they need to freshen up? 

Cats famously sleep for most of the day, but dogs  enjoy snoozing almost just as much. On average, an adult pooch sleeps between 12 and 14 hours a day.

This varies according to a number of factors, such as age, size, and of activity, according to Sleep.org. Large dogs and puppies can need up to 20 hours of rest to make up for all the energy they use up, while smaller breeds like Chihuahuas can get by with far less.

Half of a dog's sleeping is done during the night, with the rest happening at irregular intervals during the day.

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But many owners often find it difficult to predict when their pets will be active because of irregular sleeping times.

LiveScience says they do. Much like humans, dogs go through REM (rapid eye movement) sleep phases and non-REM phases.

Both can produce dreams, but REM sleep is deeper and that's when you might notice your pooch twitching, moving its paws, or making strange sounds – but it's best to let sleeping dogs lie.

As Professor Stanley Coren from the University of British Columbia tells LiveScience, dogs spend about 12% of their snoozing in the REM phase, in which the most memorable dreams usually play out: "What we've basically found is that dogs dream doggy things."

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Based on studies mentioned by Coren, sheep dogs could really be counting sheep and retrievers might be dreaming of playing fetch.

If dogs spend their nap times replaying their favorite activities, it's no wonder they always wake up itching for more of the same.