You're aching for sleep at 2pm - and raring to go at 2am. At breakfast, your appetite has gone AWOL, yet you wake up starving at midnight. Welcome to jet lag, the price we pay for a trip to the other side of the world. Aviation science can get us from Paris to Sydney in about 20 hours, but it hasn't found a quick way to reset a disrupted body clock.
So far, melatonin is the closest thing we have to an anti-jet-lag pill. Available on prescription, it's a supplement of the hormone that is produced by the brain's pineal gland to help us feel drowsy and ready to sleep.
''It's worth a go for helping you get to sleep at your destination,'' says the medical director of Travelvax Australia, Eddy Bajrovic. ''Studies have found melatonin can help reduce jet lag for people crossing five or more time zones, but the effects vary from person to person and it doesn't work for everyone.''
The timing of melatonin is important, says Professor Leon Lack, from the school of psychology at Adelaide's Flinders University. He suggests taking one to three milligrams of melatonin at bedtime if you're flying west. If you're flying east, take it at bedtime for the first two nights, then make the timing of the dose progressively earlier over the next three to four nights until you're taking it at about 7pm.
So, for instance, if you take it at 10pm on the first two nights, take it at 9pm on the third night, then 8pm the following night and so on.
Keep lights low in the evening - bright light suppresses the brain's natural production of melatonin. Knowing when you need it turned on is part of counteracting jet lag.
If you reach your destination at 6am, for instance, get as much sunlight exposure as possible through the day to suppress melatonin and help you stay awake until bedtime, says Bajrovic, who suggests going for a walk and doing something stimulating. Keep any naps as short as possible, about 30 minutes.
If you arrive in an area where sunlight is in short supply, such as northern Europe in winter, an alternative could be spectacles designed to emit light into the eye, mimicking the body clock-resetting effects of sunlight. These spectacles, developed at Flinders University by Lack and colleague Dr Helen Wright, should be commercially available next month.
It also helps to try to reduce anything that makes jet lag feel worse, including the dehydrating effects of long-haul flights.
''We dry out more quickly in an airconditioned atmosphere and, although airlines try to humidify air inside the cabin, dehydration can still be a problem,'' Bajrovic says. ''Drinking water and avoiding alcohol and caffeine will help you stay hydrated.''
Minimising fatigue helps, too. Bajrovic suggests booking long-distance flights that get you to your destination at bedtime rather than early in the day, having a good night's sleep the night before departure and getting as much sleep as possible on the plane.
What about a pill to help you sleep on long flights? Check with your doctor - sleeping pills and planes aren't a good mix for anyone at risk of deep-vein thrombosis.
''It's not just older travellers or those who've already had DVT who are at risk, but also women taking contraceptive pills, anyone who's overweight, at risk of heart disease or who has cancer, and anyone who's flying home injured from a skiing trip with their leg immobilised in plaster,'' he says.
And sleeping pills to help with jet lag at your destination? ''They can help you sleep but there's no evidence they have a direct effect on body-clock timing,'' Lack says.
Paula Goodyer blogs atsmh.com.au/chewonthis.