Somewhere off the North African coast the Tannoy crackled out a request: “Any doctor on board, please make yourself known to cabin crew.” Most medics harbour a secret apprehension about such scenarios when flying, and I have to confess that I paused for a few seconds. No one else sprang to their feet, though. My post-holiday, carefree mood was over.

A plump, middle-aged Asian woman was slumped in her seat near the front of the cabin. She was hyperventilating; her eyes were closed and she was making only inconsistent responses. She seemed to be travelling alone; certainly none of the startled people in the vicinity owned up to knowing her. It’s hard to convey quite how difficult it is to examine someone in the middle of a row in economy class. Somehow, the cabin crew and I managed to extract her and lie her in the aisle.

I set about checking her over, trying to ignore the passengers craning over the seats to take photos on their phones. Initially I was worried about a blood clot lodging in the lung, but the woman’s condition quickly improved, and we found enough English in common for me to start honing down the possibilities. By the time a stewardess came to ask whether the captain should divert to Faro in Portugal, I had a pretty good idea it wouldn’t be necessary.

Flying at altitude presents physiological challenges: cabin pressure typically equates to conditions on top of a 6,000-foot mountain (Britain’s highest peak, Ben Nevis, is around 4,400 feet). This causes a drop of roughly 10 per cent in blood oxygen saturation, which healthy people won’t notice, but if someone has significant heart or lung disease, or if they’re very anaemic, they may run into problems.

My patient did indeed appear anaemic. Beyond this, flying can generate significant psychological stress – being trapped in a speeding metal tube six miles up is deeply unsettling to some, to say nothing of the reasons why one might be travelling. My patient was visiting a gravely ill relative. The combination of hypoxic symptoms and underlying anxiety had sent her into full-blown panic.

That ought to have been it: none but the most globetrotting medic would expect to encounter more than one airborne emergency in their life. I was relieved mine had been so benign. (In 1995 the orthopaedic professor Angus Wallace and his colleague Tom Wong had to insert a chest drain to relieve a potentially fatal collapsed lung in a female passenger. They improvised the drain out of a coat hanger and a urinary catheter, sterilising it in Courvoisier cognac before operating.)

So, I felt jinxed when, on another flight, the Tannoy broadcasted the same request. This turned out to be a Londoner in his sixties who’d had nasty gastroenteritis in the days before travelling. He’d felt really poorly at the airport in Morocco, but had been patched up with an anti-sickness injection by a doctor there and allowed to fly in spite of dehydration.

We’d already begun our descent when he collapsed, so I got the captain to radio ahead to have an ambulance meet us on landing. This involved the plane taxiing to a special apron well away from the main terminal. The rest of the passengers disembarked from one end, while I stayed behind to transfer the patient’s care to the paramedics.

By the time the ambulance finally drove off, the entire flight crew had disappeared. I was left to find my own way through the deserted maze of night-time Heathrow’s airside corridors. I caught up with my fellow passengers at baggage reclaim – our luggage was having to be recovered manually, which took absolutely ages – and was berated by a man furious that my actions had caused him such delay.

This July I’m heading for Zambia, my first long-haul flight since then. Believe you me, I wish everyone on board a safe and healthy trip.

Phil Whitaker is an award-winning author. His next book, “Sister Sebastian’s Library”, will be published in 2016