What is jet lag?
Jet lag is a temporary disorder that causes fatigue, insomnia, and other symptoms as a result of air travel across time zones. A person who travels between different time zones need time for his or her internal body clock to reset itself and adjust to the new time zone. The body usually develops a set pattern of times when it is used to eating, sleeping, working,
and performing other activities. Jet lag occurs because the body is reacting to a change in the schedule of normal activities.
Our bodies naturally develop a certain sleep-wake cycle that is tied to the patterns of light and dark in our environment. Most of the body's regulating hormones follow this cycle, known as circadian rhythm. In Latin, circa means almost and dies means day. These cycles are not by themselves exactly 24 hours long, hence the "circa." Each chemical has its own cycle of highs and lows, interacting with and influencing the other cycles. Body temperature, sleepiness, thyroid function, growth hormone, metabolic processes, and the newly discovered sleep hormone melatonin all cycle with daylight. There is a direct connection between the retina (where light hits the back of the eye) and the part of the brain that controls all these hormones. Artificial light has some effect, but sunlight has much more.
When people are without clocks in a compartment that is completely closed to sunlight, most of them fall into a circadian cycle of about 25 hours. Normally, all the regulating chemicals follow one another in order like threads in a weaving pattern. Every morning the sunlight resets the cycle, stimulating the leading chemicals and thus compensating for the difference between the 24 hour day and the 25 hour innate rhythm.