Though we once might have stood and shuckled with fervor for all the morning prayers, now we sit and try to work up a sway. Then comes the next Rosh Hashanah with it's new injection of life and we start the cycle again. Again, paralleling the New Year in 'time' is the Temple in 'space'. So is the power of the House of Hashem. Our Sages say that sleep is one sixtieth of death.
Sleep is the antithesis of what the Temple is about.
Just as after the sin of Adam and Chava did they 'know they were naked', so too this Kohain experiences a potentially similar sensation. A reminder that there is still a blemish in the world and he's not helping to well in the reparation. Now we can understand a little better the sin of Adam. He was the raishis of soul formed from the dust of the Temple Mount, the raishis in space, and on the day of the raishis in time. By his sin he put a blemish into the aspect of raishis.