We naturally feel tired at two different times of day:  about 2AM and 2PM.  It is this natural dip in alertness that is primarily responsible for the post-lunch dip.

The post-lunch dip is a real phenomenon that can occur even when the individual has had no lunch and is unaware of the time of day.  This dip has its roots in human biology.  It is certainly exacerbated by a high-carbohydrate lunch, and may be more likely to occur in extreme morning-type individuals.

Quit Counting Sheep…Sleep with a Wolf!