Symptoms of jet lag – i.e. the time desynchronization between the internal biological clock and the external or environmental clock – are fatigue, insomnia and sleepiness, difficulty concentrating, mood disturbances, lack of appetite, gastrointestinal disturbances and performance changes. To facilitate the adjustment, it is recommended not to sleep during the flight and try to go to bed later, at local time. This will increase the pressure to sleep and delay wake-up time in order to match the local hour. Return trips should imply the contrary: the flight should be overnight and one should sleep during the trip.
Travelling east, which makes our clock walk back, has a more difficult adjustment than travelling west. In the first case it is recommended to advance the phase in the previous three days, about an hour or two every day, with morning light (5000 lux) and melatonin in the afternoon. There is a great individual variability in circadian adaptability. Night owls adapt more easily than larks.