Whether for business or pleasure, many of us increasingly rely on air travel to reach our destinations. But flying can be exhausting, and flying across multiple time zones can cause jet lag.

Jet lag is more than just being tired from traveling. Technically called circadian dysrhythmia, jet lag is a disruption of the body’s intricate biological inner-sleep cycle caused by crossing multiple time zones quickly. It occurs when the clock on the wall at your destination indicates a time far different from your internal body clock, which is still back home on its original time schedule.

You are out of sync with your environment, and that has ramifications for your alertness and feelings of wellbeing. Jet lag causes business travelers to be less productive, athletes to be less sharp and tourists to be too tired to fully enjoy their long-anticipated faraway vacations. Jet lag is not new.

Symptoms of Jet Lag:
Daytime sleepiness
: Ninety percent of travelers report experiencing daytime fatigue and sleepiness. If you give in to the urge to sleep during the day at your destination, you may not be tired enough to sleep at bedtime.

Insomnia: The next most common symptom of jet lag is insomnia. You experience difficulty falling asleep at night. Once you do get to sleep, you’ll have less deep sleep and less REM sleep. The night’s sleep is often fragmented by frequent awakenings.

Poor concentration: More than two thirds of air travelers report having poor concentration, or in severe cases of jet lag, temporary amnesia. You become unable to focus attention, cannot think clearly and have foggy memory, and your ability to write coherently is impaired.

Disorientation: Many travelers also experience disorientation. You become confused and cannot remember where you are, especially when you wake up in the middle of then night.

Slower reaction time: Many travelers suffer from slow reflexes. This seems especially relevant if you must cope with unfamiliar traffic patterns (like driving on the opposite side of the road) in your new destination.

Gastrointestinal problems: About 50 percent of travelers say that jet lag disrupts digestion. You might have a poor appetite or have hunger pangs at odd hours. You might become constipated and experience heartburn or ulcers from eating meals at hours when you would usually be asleep.

Other symptoms: Other reported symptoms of jet lag include irritability and depression, headaches, urinary system disruptions, alterations in the menstrual cycle, tendency to catch colds and changes in the effectiveness of medicines. 

Factors Influencing Your Susceptibility to Jet Lag
Number of time zones crossed
: Jet lag starts to be noticeable when you cross more than three time zones. The greater the number of zones crossed, the greater the severity of jet lag symptoms.

Direction of flight: The direction of your flight matters greatly. When you fly eastbound, or against the direction of the sun, jet lag tends to be more severe than when you fly west. You can actually take 50 percent longer to recover from jet lag after an eastward flight than after a westward flight of the same distance. When flying westward, you are allowing your body to follow its natural inclination to extend the day; remember, the body clock’s natural sleep-wake cycle is around twenty-five hours, not twenty-four. Because north-south and south-north flights do not involve time zone changes, they do not cause jet lag. You might feel physical or mental exhaustion after a long flight in these directions, but you will not be jet-lagged.

Age: The older you get, the more you are likely to experience the debilitating effects of jet lag.  Babies under age three seem unaffected, children adapt better than their parents, and the elderly seem to have the most trouble.

Sleep debt: The amount of sleep debt you are carrying can affect your susceptibility to jet lag. In general, the better rested you are, the better you’ll fare when faced with jet lag.