You'll probably have a hard time falling asleep then. In the morning, you'll likely be drowsy, since you'll be awake at hours you usually sleep. Conversely, if you go to Hawaii, you may have trouble staying up in late evening, and you'll likely wake up too early. If you have to give a talk or negotiate a contract, Smolensky says, jet lag may disrupt your ability to focus and think clearly. It also slows reflexes, hampering performance at a concert, athletic competition, and behind the wheel of a car.
Sunlight coming through the eyes is the body's most powerful time-setting cue.
It anchors internal rhythms such as sleeping and waking, and hunger, with the rhythms of our planet. These rhythms resist change. It takes roughly a day for each time zone crossed for body rhythms to shift from home time to the new local time. Jet lag usually is worse following an eastward flight than a westward one, Smolensky notes. An eastward flight shortens your day.