Jet lag or desynchronosis, is a temporary condition that some people experience following air travel across several time zones in a short period of time.
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.
This causes the traveler's internal clock to be out of sync with the external environment. Until recently, jet lag was not treated as a medical condition. It is now included as one of the 84 known or suspected sleep disorders and affects millions of people each year.
Jet lag occurs because the body is reacting to a change in the schedule of normal activities. People experiencing jet lag have a difficult time maintaining their internal, routine sleep-wake pattern in their new location, because external stimuli, like sunshine and local timetables, dictate a different pattern.
For this reason, one can feel lethargic one moment and excited the next. The result is that we feel excessively sleepy during the day or wide-awake at night. People may experience jet lag in varying degrees.
In general, the severity of jet lag symptoms is directly related to the number of time zones crossed by a flight. Jet lag symptoms typically last longer following eastward flights. Flying west results in early morning awakenings, whereas flying east usually results in difficulty initiating sleep.
All age groups are susceptible, but individuals over the age of 50 are more likely to develop jet lag than those under the age of 30. Also, individual susceptibility tends to vary considerably and it is possible that pre-existing sleep deprivation will intensify jet lag.
Jet lag is a unique sleep disorder because its onset is not necessarily caused by abnormal sleep patterns, like insomnia. Travelers who sleep normally prior to transmeridian travel is not immune to jet lag.
The symptoms result when a person’s internal clock attempts to acclimate to a new external environment. This acclimation involves circadian rhythms that, among other functions, are associated with the body’s management of sleep.
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." Most of the body's regulating hormones follow this cycle, known as circadian rhythm.
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. 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.