Period of adjustment of biological rhythm after moving from one time zone to another, experienced as fatigue and lowered efficiency.
It reflects a delay in the synchronization of changes in the level of blood cortisol, the major steroid produced by the adrenal cortex (see adrenal gland ), with the local day-night cycle. Duration and severity depend on how much distance is covered in how little time. Travel by jet, after which the phenomenon may persist for some days, first made it noticeable, accounting for the name.