Jet lag is a physiological condition that results from alterations to the body's circadian rhythms caused by rapid long-distance trans-meridian (east–west or west–east) travel. For example, someone flying from New York to London, i.e. from west to east, feels as if the time were five hours "earlier" than local time, and someone travelling from London to New York, i.e. from east to west, feels as if the time were five hours "later" than local time. Jet lag was previously classified as one of the circadian rhythm sleep disorders.