There is no such thing as which side of the face gets bigger when you sleep on your side. A large face on one side may be the result of congenital developmental abnormalities, an enlarged bite muscle, mumps, etc. In the case of children, there may be the case of sleeping on the side, one side of the face becomes smaller. Sleeping on the side is a sleeping position that many people choose in life, but there is no such thing as which side of the face will get bigger when sleeping on the side. For adults, the sleeping position does not affect the facial bone structure. Therefore, if there is asymmetry between the two sides of the face, it may be caused by congenital developmental abnormalities, such as congenital deviation of the jaw, craniomaxillofacial deformity, and so on. Secondly, it may also be due to the fact that usually always use the same side to chew food, resulting in biting muscle hypertrophy, so visually you will think that one side of the face is big and the other side is small. Besides, it may also be caused by parotitis which results in localized lymph node enlargement. However, in the case of children, there is a possibility that sleeping on the side may affect the facial bone structure. If you sleep on your left side for a long time, the left side of your face will become smaller because of the compression, and then the right side of your face will appear larger. In conclusion, you need to sleep in a proper position. If you have a large or small face, you need to go to the hospital in time to find out the exact cause.