The feelings of disorientation encountered as a result of crossing time zones are known as jet lag. Symptoms include fatigue and general tiredness, inability to sleep at night, loss of concentration, loss of drive, headaches and general malaise.
Jet-lag occurs when biological rhythms are disrupted as a result of rapid transitions across multiple time-zones. Such desynchronization of rhythms also occurs in nocturnal shift work employees who transfer to night shifts.
A classical rhythm is represented by a sine wave, fluctuations occurring cyclically about a mean value rising to a peak and half a cycle later dropping to a trough. Twenty-four hour rhythms are known as circadian (about a day). An example of a biological rhythm is core temperature. We can find the characteristics of rhythms using the mathematical technique of cosinor analysis to determine the mean, the peak, the amplitude, and the time the peak occurs (the acrophase).