Domestic cats can rarely be accused of overexerting themselves. Cats seem genetically programmed to sleep. In fact, cats can sleep as much as 16 hrs a day and older cats may sleep 18-20 hrs a day1!
Sleeping helps cats conserve energy, but they probably are not “sleeping” as much as you think.
Cats also have a unique sleep/wake cycle. Learn more about it here.
One of the things I still enjoy most is watching my cats as they dream. They seem to run in their sleep at times and often chatter and vocalize— they may be chasing an imaginary butterfly or lizard.
It is common for cats to snore when sleeping. My own cat will often cover his eyes and in a few minutes he is sawing proverbial logs.
All of these sleep associated behaviors of cats are normal to one degree or other. It is important as with other behaviors to be familiar with what is normal for your cat. Changes in sleep habits can be associated with a variety of factors, but should be observed and evaluated by your veterinarian as part of your cat's annual physical evaluation.
Samantha. "How Much Do Cats Sleep?" How Much Do Cats Sleep? Selected from Animal Planet, 19 Mar. 2011. Web. 12 Aug. 2015.