Cats roll themselves up when sleeping because this position is more comfortable, they feel cold, or they don’t trust the surrounding environment. This is a normal phenomenon. Generally, cats and dogs will roll themselves up to sleep, so that they are sleeping You will feel more secure.
Tip:
If the cat rolls up itself while trembling while sleeping, then It means it is cold, and you need to pay attention to keeping the cat warm to prevent the cat from catching a cold.