H.M.
When I taught preschool and we had certain kids who had a harder time falling asleep, but still needed that down time, we moved them to a less distracting part of the room, had them bring a blanket or stuffed animal from home and spent some extra time rubbing their backs or playing with their hair, gently rubbing on the bridge of their nose always helped too, not to mention the soft lighting and music in the background. Talk to his teachers and see what they suggest doing to help!