When we travel from a place on earth, of one time zone to another place of a different time zone, crossing various time zones, our body’s sleep-wake clock cycle will be  disturbed. This sleep-wake clock cycle disturbance is called "Jet lag". 

Jet lag will normally lead to:-

• fatigue,
• dehydration,
• disorientation,
• lack of concentration and motivation especially for activities that require cognitive skills such as reading or negotiating a business deal.

Crossing different time zones is the major cause of jet lag. However, it is not the only cause for the same. The time taken for the adjustment of our body’s sleep-wake cycle due to the travel from one place of a time zone to another place of a different time zone, crossing different time zones, will depend on:-

• the time zones of the starting point and the destination,
• various time zones crossed,
• the period of continuous travel, 
• rest taken during the travel,
• time of sleep in between and
• the nature of our body in adjusting the sleep-wake cycle.

We will require one day per one-hour of time difference, in various time zones crossed to regain normal rhythm and energy levels. Depending on the time difference we will require number of days to recover from this sleep clock disturbance which is called “Jet lag”. however, this will vary from person to person, depending on the body conditions.A few things that cause jet lag, can make our flight miserable. Being stressed, nervous or hung over during the flight are some of them. Also taking coffee, tea and alcoholic drinks in-flight will affect our sleep. Remaining glued to our seat for hours, airline food and stale cabin air will add to the problem.

If we are frequent fliers crossing different time zones, We must:-

• drink a lot of water and not coffee, not alcohol, not even juice,
• try our best to sleep,
• start trying to sleep during takeoff, which is a natural sleep inducer,
• use blankets, pillows, earplugs etc.,
• keep our feet up, if possible, and
• eat lightly when we are onboard.

There is no sure remedy for jet lag/sleep-wake clock disturbance. However, while we are onboard, we must set our watch to match destination time. Sleeping pills are not advisable, which can induce a comatose state and make us more prone to developing disturbance in blood circulation in our legs. We must stretch our legs, walk around as much as possible and try to freshen up during stop-overs. Once we reach our destination, we may start eating and sleeping on the new schedule.