Jet lag is a physiological condition caused by an alteration to the body's biological clock caused by rapid trans-meridian travel on a jet aircraft. Our biological clock,Known as the circadian rhythm,is controlled by a tiny part of the brain called the hypothalamus,which activated various body functions such as hunger,thirst and sleep during a 24-hour cycle.lt also regulated body temperature,blood pressure and the level a hormones and glucose in the bloodstream.