A Victoria University sleep psychologist says a holiday can bring a surprising level of tiredness for some, despite more sleep than usual every night.
Professor Dorothy Bruck suggests that while most people expect to feel more energised during their holidays, some paradoxically feel more tired.
The demands of the festive season can leave people "over-revved," and the body may use the holidays as simply a chance to catch up on sleep, she said.
"If you haven't been fully rested for a while, you can forget what it feels like.”
While the average amount of sleep for adults is about 7.2 hours, when people sleep until they can't sleep anymore, the amount increases to 8.25 hours. So when sleep time is less limited while on holidays, the body seeks its deficit hour of sleep to rebuild and restore.
"People think sleep is just a knockout time, when nothing happens but we know that certain parts of the brain use more oxygen and glucose during sleep."
“People need to prioritise sleep a little more because it’s as important as healthy food and exercise.”
In addition, the afternoon siestas that many indulge in on holidays are the body’s way of accommodating a mid-afternoon dip that is a normal part of circadian rhythms, or the biological clock that influences wakeful or sleepy periods.
However, excessive napping is not recommended even during holidays as naps that last longer than 20 minutes can weaken the body's drive to sleep at night, she said.
Holiday festivities can also upset slumber.
Alcohol, for example, can affect sleep quality, even well after consumption.
While a couple of drinks may disrupt only that night’s sleep, binge drinking (five or more standard drinks in one night) can sabotage sleep for up to a week, she said.
Digestive discomfort can also be a sleep-killer, particularly high-sugar foods just before bed that can produce a temporary “sugar-high” that prevents immediate sleep.