If you better understand what is at stake in jet lag, you will be better able to adjust harmoniously. Jet lag is reasonably well explained scientifically today. Rapid changes of time zones disturb the functioning of your body clock, which remains stubbornly set on departure time for a while. This can make sleep shallow or nonexistent for substantial parts of the night while vigilance is less than optimal during parts of the day. Flying west seems easier than flying east. Jet lag can in some cases be a more serious medical nuisance.