Eye fatigue needs rest, body fatigue also needs rest, and brain fatigue also needs rest. When we take a nap, after all the functions of the body are fully rested, our memory will be improved and our recognition ability will be improved when we wake up. I had the same experience. Long-term mental work can lead to brain fatigue, and sometimes I can't think of some ideas or even forget words. But after the age of 5, my brain can better think of some solutions and countermeasures to deal with the next work after a short rest.
The correct nap posture is actually head high and feet low. You can choose to sleep on your right side. People like pillows because their heads are high and their feet are low. The reason why they choose to lie on the right side is mainly to relieve the pressure on the heart by lying on the side. Our heart is usually on the left side, so lying on the right side can effectively reduce the occurrence of heart compression.
Of course, lying flat is also a correct sleeping position. For example, some people sleep in a big position. Personally, I especially like this way of sleeping, because the whole body can relax, and many children like this way. After all, it's very comfortable and won't feel oppressive.