The eyelids close. Air is pumped out from the space between lid and cornea, causing a change in air pressure which pulls the eyeballs out slightly. Said action disengages clutch in anterior vertical skull shaft, causing breathing wheel to spin freely. As head leans back, somnolence gears fall into place; air pressure balance is reestablished; clutch reengages. Breathing wheel is slowed but provides more power to respiratory system. Spark plugs, now deregulated, also fire at slower rate, producing more chaotic but lower-level neural impulses.[1] Outlying motor systems are disconnected from main electronic system to avoid undesirable intermittent external impulses. At this point we declare the head system's state to be "asleep."

[1] In newer systems spark plugs are relatively unregulated during "waking" hours, also.