What cats do when sleeping...

Cats conserve energy by sleeping more than most animals, especially as they grow older. Daily durations of sleep are various, usually 12–16 hours, with 13–14 being the average. Some cats can sleep as much as 20 hours in a 24-hour period. The term cat nap refers to the cat's ability to fall asleep (lightly) for a brief period and has entered the English lexicon – someone who nods off for a few minutes is said to be "taking a cat nap".
Due to their crepuscular nature, cats are often known to enter a period of increased hyperactivity and playfulness during the evening and early morning, dubbed the "evening crazies", "night crazies" or "mad half hour" by some. [10] [11]
The temperament of a cat can vary depending on the breed and socialization. Shorter haired cats tend to be skinnier and more active, while cats with longer hair tend to be heavier and less active.
The normal body temperature of a cat is between 38 and 39 °C (101 and 102.2 °F).[12] A cat is considered febrile (hyperthermic) if it has a temperature of 39.5 °C (103 °F) or greater, or hypothermic if less than 37.5 °C (100 °F). For comparison, humans have a normal temperature of approximately 37 °C (98.6 °F). A domestic cat's normal heart rate ranges from 140 to 220 beats per minute, and is largely dependent on how excited the cat is. For a cat at rest, the average heart rate should be between 150 and 180 bpm, about twice that of a human.

SmellA domestic cat's sense of smell is about fourteen times as strong as a human's. Cats have twice as many smell-sensitive cells in their noses as people do, which means they can smell things we are not even aware of. Cats also have a scent organ in the roof of their mouths called the vomeronasal, or Jacobson's, organ. When a cat wrinkles its muzzle, lowers its chin, and lets its tongue hang a bit, it is opening the passage to the vomeronasal. This is called gaping, "sneering", or "flehming". Gaping is the equivalent of the Flehmen response in other animals, such as dogs, horses and big cats.