It's one of the drawbacks for anyone setting off for far-flung places: How bad will the jet lag be when you get there?
Those feelings of tiredness and disorientation could become a thing of the past, however - thanks to what are claimed to be the world's first “time-control” spectacles.
The high-tech glasses emit a soft green glow which is said to work on the human body clock to change our sleep patterns.
Using the device, called the Re-Timer, means long-haul air passengers can step off the plane feeling fresh, even after a flight from Britain to Australia, say the sleep researchers who created it.
Inventor Professor Leon Lack said the glasses could also help insomnia sufferers, keep shift workers more alert and get teenagers out of bed in the morning.
“The light from Re-Timer stimulates the part of the brain responsible for regulating the 24-hour body clock,” said Professor Lack, of Flinders University in Adelaide, South Australia.
“Using a light device allows you to transition your body clock to a new time zone in small steps. This eliminates the sudden change people experience after flying and reduces the symptoms of jet lag.”
The scientists say the light exposure changes the behaviour of a gland at the base of the brain which controls the body clock.
It sends signals to the rest of the body, triggering the production of hormones, which create daily cycles known as circadian rhythms.
Those who wanted to sleep and wake up earlier should wear the device for 50 minutes in the morning, while those who want to sleep and wake later should wear them for 50 minutes before bed to delay the body clock, say the researchers.
The battery-powered glasses, which are on sale in the UK on the Re-Timer website for £162, can be worn while completing normal daily tasks such as working on the computer or reading.
Almost 94 percent of passengers experience jet lag after a long flight.
This is because travelling through different time zones confuses the body clock, which uses cues from the outside world -- such as light, dark, silence and noise -- to tell the body when it should be asleep or awake.