Jet lag is a condition marked by fatigue and irritability as a result of air travel across several time zones.

Living organisms are accustomed to periods of night and day alternating at set intervals. Most of the body's regulating hormones follow this cycle, known as circadian rhythm. Body temperature, sleepiness, thyroid function, metabolic processes, and the 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.

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.

Today, technology has surpassed adaptability...