A cat curling up in a ball while sleeping may be due to cold infection, unfamiliarity with the surrounding environment, or because it feels comfortable in this position. Generally, there is no big problem and it is a normal phenomenon, so don’t worry, just pay attention to keeping the cat warm. Yes, prevent cats from catching colds. Most cats like to curl up in a ball to sleep, because this sleeping position is more comfortable and helps to adjust their physical condition.