I came to the comments to state exactly your first line. When I served in the German army, no combat involved, the amount of physical activity was at a very hig

I came to the comments to state exactly your first line. When I served in the German army, no combat involved, the amount of physical activity was at a very high level, so I was basically constantly tired and was able to fall asleep in under 30 seconds, even when sitting in the classroom.