As we all know, water always flows downwards, and so does blood. When you don't put the pillow on your head, blood will flow to your head because your head is lower than your heart. After a long time, your head will feel uncomfortable. Moreover, blood will flow to the head, the heart will beat fast, and people will not fall asleep easily. If you sleep with a pillow and your head high, people will feel more comfortable, blood will flow slowly from bottom to top, and your heart can rest for a while. Therefore, it is best to sleep with a pillow.