Cats sleep unlike people and dogs. It may look as if they are fast asleep but the tiniest sound will rouse them to complete alertness. After about 10-30 minutes of this semi-sleep, they will fall more deeply asleep called paradoxical sleep because the brain waves during this time are oddly more like wakefulness. These 2 different patterns of sleep will alternate if sleep persists.
During paradoxical sleep the cat’s body relaxes completely although individual muscles may contract suddenly, eye movement may be observed, tail and whiskers may twitch. All of this leads us to believe that cats are dreaming but no one knows for sure.
Cats who are bonded with one another, usually littermates or kittens raised together will sleep entwined. This is never true for cats who are not considered family. Cats don’t trust cats they haven’t known for as long as they can remember.
Sleeping curled up, feet relaxed, tail wrapped is the sign of a cat who feels no cause for alarm. This position is indicative of feeling safe.
Sleeping with all four feet under the body has a couple of possible interpretations. The first instinct of a cat when challenged is to flee. All four feet tucked under the body may indicate a sense of pending threat; it is the position from which one could flee most readily. Sleeping or resting in this position though may indicate a cat with serious health problems, however. Cats when they are having trouble breathing will continue to breathe through their noses with the mouth closed, rarely panting. In order to keep the chest from being compressed, a cat with lung problems like pneumonia or fluid in the chest will keep their chest elevated on their paws and off the floor or bed. This can also be an indication of abdominal pain for the same reason.
Cats who appear to be resting but have one eye open are keeping an eye on their environment because something is amiss.
Sleeping under the covers is a personal decision. Some cats wouldn’t be caught under covers, EVER. Others like the warmth and the warm human next door.
Few cats sleep on their backs. It is a position of great vulnerability not the least because so much time would be required to get into position to flee.