Venetia Sherson has some advice for the jet-lagged.

There are several things you should not do when jet-lagged. One is drive; another is mess with the man from Avis. I have done both, and am wiser for it.

We arrived at Glasgow Airport after a 30-plus hour flight from Auckland. Customs was smooth; the people polite and the queues short. True, I did walk into the men's toilet and nodded off beside the luggage carousel. But I thought I was good to go. Until I met the man from Avis.

"Welcome to Glasgow," he said, with a charming Scottish brogue. I smiled and gave him our reservation number. "Unfortunately, we don't have the Vauxhall Astra you ordered in New Zealand. But we do have similar vehicles."

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No problem. His eyes still looked kind. We chose our car. I returned to the man with the smiling eyes. "The car doesn't have a satnav unit," I said. Still polite. We were heading to a dot of a spot on the southwest coast of Scotland. Mobile service could be dodgy. He looked at his notes. "That will be an extra £99," he said. "I already ordered and paid for it online," I said. "But this car doesn't come with satnav," he countered. "There is an extra cost."

I felt the beginning of a tic in my sleepless left eye. "Could you check the reservation?" He glanced at the computer and smiled. "No record of a satnav." His eyes looked harsh and ferret-like. I gripped the handle of my case. I was not about to pass out with exhaustion. I saw us miles from nowhere, in a forest, without signposts or friendly locals who could point the way.

I reached into my bag, brought out my phone, typed Avis into the email search and let out a triumphant whoop. Under the Extras that included "roadside assistance", and "fuel upfront", was "Avis GPS" with a tick inside the box. Amount paid £90.93, a month before departure. I gave him my nice-traveller smile as he gave me the GPS kit.

"Could you give me directions to our hotel?"

We are responsible travellers. We know not to get behind the wheel after flying for the best part of two days. But the hotel was one block away, within walking distance of the airport. We could handle that. The man from Avis was ready to move on. "You can see it from here," he pointed vaguely out the window. Pride stopped me from asking, "Where, exactly?" Besides we had a satnav. How hard could it be?

Two minutes later, we were on the M8, heading towards Edinburgh, 70km away. The M8 is the busiest motorway in Scotland and one of the busiest in the UK. It is no place for weary travellers. I saw a headline, "Elderly couple cause pile-up; jetlag blamed."

My husband swore. I was the navigator. I pointed to an offramp that took us to a greenfield suburb with no sign of habitation. "I figure, if we get back on the M8 in the opposite direction, we'll get back to the airport," I proffered. The driver was too tired to argue. Ten minutes later, we were back in the rental car lot. It felt like home. I climbed up on a bollard. "I can see the hotel," I said. We crept from the carpark, took a left, instead of right and rolled up to the hotel door.

The next day Satnav directed us to our destination along single-lane forestry roads, where there were no signposts, nor people, and which took far longer than the two hours Google estimated. I imagined the Avis man smiling.

• Jet lag is caused by disrupting your circadian rhythm, the internal body clock that regulates sleep and waking. Symptoms include fatigue and disorientation, confusion, and getting uptight. It can take five days to fully recover. Experts advise to get a good night's sleep before you drive or discuss a business deal.

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