As I climb the path, the ground falls away on my left. The path narrows, the ground falls away more. It steepens to my right. Soon there is nothing but fresh air on my left and a rock wall on my right. A knot has started in my belly – just a small knot, a tightening somewhere inside. Then my knees – a wobble. Clamminess next; then dizziness; then, “Sit down. Now!” Sitting on a narrow path with back pressed against rock and legs dangling down a vertical drop. Nightmare.

“Trace it back to the first time. When did it start?” I want it to be logical. But logic is too slow for emotion in the race for fear. Logic can pull fear back, can try not to let it get away, while emotion bubbles and troubles and blasts its way forward.

It only happens on the way up, never on the way down. Up is a problem, down is a doddle.

I dealt with it years ago. I don’t sit down now. Sometimes you’ve just got to climb. Wider paths. Avoid narrow ones if you can. Walk close to the wall. Hand holds. Stick on the outside pushing inwards.

But I often feel it start – recently on a mountain in New Zealand – small mountain, big feeling.

High buildings – stand back from the window. High bridges – that feeling of falling with nothing beneath, over and over and over. As for the London Eye – I sat on the bench in the middle of the pod – fantastic views through shaded eyes.

Might there be a cause – a reason – an explanation? Aged three, I watched a man climb a cliff. Towards the top, he stopped. He fell backwards. I see him now, sailing through the air, bouncing against the rock face. I don’t remember the end.