Doctor-patient articles related to symptoms and diagnosis:
Modern humans often find themselves desynchronized from their internal circadian clock, due to the requirements of work (especially night shifts ), long-distance travel, and the influence of universal indoor lighting.  Even if they have sleep debt, or feel sleepy, people can have difficulty staying asleep at the peak of their circadian cycle. Conversely they can have difficulty waking up in the trough of the cycle.  A healthy young adult entrained to the sun will (during most of the year) fall asleep a few hours after sunset, experience body temperature minimum at 6AM, and wake up a few hours after sunrise. 
Mixture of feed ingredients are solid at room temperature, therefore, the extrusion process of these ingredients requires a temperature higher than this in order to soften or melt the mixture and allow for fluidity through the barrel.  In the United States, before entering the extruder, water is added to the starch mixture to elevate the moisture content to 20 to 35%.  During the extrusion process, the high amounts of pressure applied to the mixture forces it to enter through the die before exiting the extruder completely.  The material is put through high amounts of shear stress that generates heat which allows for mixture to come together.  Temperature in the extruder is raised to above 100 degrees Celsius by the use of steam, hot water, or other heat sources.  The pressure is increased to allow starch granules to gelatinize.  Fat used in US extruders is then added into the mixture at the metering zone of the extruder which allows for the incorporation of fat, but without affecting the product's ability to expand.  Feed mixture stays in the extruder for only 15 to 120 seconds before exiting through die openings.  As the feed exits the extruder, it is subjected to relatively lower amounts of heat and pressure, that results in the expansion of the product, creating its “puffed” kibble appearance.  The feed is expelled in one long sequence where it is cut to its desired size by a rotating fly knife.  As moisture of this extrudate is at roughly 20 to 35% of its weight, it is dried further in an oven to reduce its moisture content to 8 to 10%.