Jet lag (desynchronosis) is when your internal clock gets messed up due to crossing time zones too quickly, i.e., by plane. The problem occurs because your body is not used to the new daylight and darkness patterns.
This means that if you are traveling north/south along the same timeline, jet lag will not occur, no matter how long the flight is. Of course, you may not feel 100% due to a number of reasons, jet lag just won’t be one of them in this case.
For most people, jet lag is only a problem when crossing two or more time zones. The time it takes for the body to adjust is dependent on the person and the number of time zones crossed.
Fatigue and/or insomnia are the major symptoms. Others may include:
Anxiety.
Constipation.
Diarrhea.
Irritability.
Nausea.
Most people can expect their bodies to adjust at a rate of one or two time zones per day. This process can be made faster by helping the body adjust to the new time zone.
Change your watch to the new time zone and synchronize your routine to this new time zone including eating, exercising, sleeping, using the bathroom etc.
If you must nap, only do so for a maximum of an hour.
Avoid alcohol, caffeine and other drugs, including sleeping aids.
Keep hydrated.
Move about the plane.
If able, you can start this process a few days before you take off. In doing so, your body will not have to make such a big adjustment:
Ø If traveling east, go to bed an hour or two earlier.
Ø If traveling west, make it an hour or two later.