I just got back last week from six weeks in Tanzania and I am jetlagged.
The official medical term for jetlag is circadian dysrhythmia. Basically when you travel across several time zones your body's daily patterns get maladjusted. Sunlight is the normal mechanism for setting the times for eating, sleeping, and body temperature. And when you're in a time zone that differs by six to 12 hours your body is way off. Three hours? Not a problem. By the way traveling east is much harder to adjust to than traveling west. And it's not a matter of the time of the airplane flight, going north to south great distances is no problem -- it's east-west travel.
There is a tiny organ buried between the hemispheres of your brain that is affected by light -- the pineal gland. Shaped like a pinecone and the size of a grain of rice it controls your daily rhythms by directing the release of hormones that regulate many functions. Long recognized as very important, Rene Descartes dubbed the pineal the "principal seat of the soul," suggesting it connected the body and intellect.
In the "The Snow Leopard" by Peter Mathession, he and biologist George Schaller were trekking in the Himalaya Mountains searching for the elusive cat. And suddenly all of their Sherpas just sat down and refused to move.
"What are you doing?" asked Schaller.