Babies always shake their heads when they lie down for the following reasons:
First, the child who shakes his head may be looking for his mother's nipple. Many mothers will think that their baby is hungry when they see it crying at night, and then feed it. In fact, this is a very bad habit, which will cause children to wake up at night and have the habit of breastfeeding.
Second, one of the main reasons why the baby likes to shake his head while lying down is that the back of his head itches and his skin itches. They can't catch it with their hands, so they can only shake their heads to relieve it. The friction between scalp and pillow can relieve itching symptoms.
Third, I am too excited before going to bed and will shake my head. Let the baby calm down within 0.5 to 1 hour before going to bed. Don't be too excited before going to bed, and don't tease your baby too much, lest your baby be too excited and nervous to sleep.