The chill begins almost as soon as the cabin door seals. A passenger, perhaps flying out of Tehran or Jakarta, reaches for a thin blanket or a jumper they have learned to carry, even in summer. The air is not merely cool; it is desert-dry, with humidity often hovering between 10 and 20 per cent, a figure lower than that of many of the world’s arid zones. Aviation experts in Iran note that this is not a cost-saving measure but a deliberate safety design: at cruising altitude, cabin pressure is equivalent to standing at around 2,000 metres, where the body receives roughly a quarter less oxygen than at sea level. A warmer cabin would dilate blood vessels and increase the risk of passengers fainting, particularly when they stand suddenly after a long sleep. So the cold is a quiet guardian, a discomfort that keeps consciousness tethered.

That same body, however, is soon asked to perform a more complex negotiation: the resetting of its internal clock. Travellers crossing multiple time zones, such as those on the long Jakarta-to-Europe haul, are advised by Indonesian travel specialists to choose flights that land in the late afternoon, ideally between 2 p.m. and 5 p.m. local time. The reasoning is simple: a dose of natural light and light activity before nightfall helps the brain’s master clock adjust faster. On board, the ritual begins early. Seasoned passengers change their watches to the destination time the moment they settle into their seats, forcing themselves to sleep or stay awake according to a rhythm that does not yet exist in their cells. They drink water obsessively, shun alcohol, and walk the aisles to keep blood moving, small acts of discipline against a force that can leave them hollow-eyed and foggy for days.

Yet the struggle for alertness is not confined to the air. On the ground, in offices across Lagos and Abuja, a different kind of fog descends after the midday meal. Postprandial somnolence, the so-called food coma, is a familiar adversary. Nigerian health observers describe a scene that repeats daily: heads nodding in meetings, the hum of air conditioners becoming a lullaby. The culprit is often a plate of pounded yam or white rice, high-glycaemic staples that send blood sugar soaring and then crashing. The remedy, nutritionists in the region suggest, is not to surrender to a sofa but to take a short walk, drink a glass of water, and, crucially, rethink the composition of the meal itself—more fibre, more protein, smaller portions. The body, it turns out, can be retrained even in the face of the heaviest stews.

At night, the disquiet continues. A sweeping study by the US National Sleep Foundation, drawing on 190 million nights of smart-bed data, found that 70 per cent of American adults report difficulty staying asleep. Racing thoughts, physical discomfort, noise, and temperature all conspire to fragment rest. In Indonesia, the phenomenon of sleep paralysis—known locally as ketindihan—leaves sufferers momentarily trapped between wakefulness and dreaming, fully conscious but unable to move or speak, sometimes sensing a weight on the chest or a shadowy presence. It is a terrifying glitch in the transition between states, a reminder that the border between sleep and waking is thinner and stranger than we like to believe.

What threads these experiences together is a quiet accumulation of traveller’s knowledge, a folk physiology passed from flight attendant to passenger, from office veteran to new recruit. A flight attendant writing for a US business publication advises against buying bottled water at the airport: bring an empty bottle and fill it after security. A Spanish daily warns that arriving late or packing too heavily can turn a cheap ticket into an expensive ordeal. An Argentine industry report reveals that mishandled luggage still costs airlines $6.3 billion a year, but that the integration of Apple’s Find My function with baggage-tracking systems has cut permanently lost bags by 90 per cent. In the end, the image that lingers is not one of chaos but of small, deliberate adjustments: a passenger on a night flight, watch already set to a future time, taking a slow walk down the dimmed aisle, the body learning, step by step, to inhabit a new hour.