It started with a joke. The previous day I had developed numbness in my left hand and foot and on the left side of my tongue. After being fobbed off by an avuncular locum GP (“nothing to worry about, old chap, come back in a couple of days”), I called my friend and writing partner Phil Hammond, a doctor. I told him my symptoms.

There was a pause. That was worrying because Phil rarely thinks before he speaks. “Are you telling the truth?” he asked.

“Of course.”

“In that case, mate, you’re ****ed.”

It wasn’t a very good joke.

There wasn’t a great deal to laugh about after that, though I tried. The next day was spent falling over and being sick — but I was a television producer: I always spent Edinburgh Festivals like that.

Getting behind the wheel turns my sweet wife Michele into Stirling Moss. Whizzing her sick man to an emergency MRI scanner turns her into Jeremy Clarkson on a diet of raw liver and testosterone pills.

I had acquired or developed or caught (no one knows which, even now) a demyelinating lesion, deep in my brain stem. A lesion refers to abnormal tissue in the body. In my case, it was stripping the brain stem of myelin.

Myelin is a useful thing. It coats nerve cells, like the plastic coating on a wire. Without it, well, don’t switch on your toaster. In my case, the investigations showed that it had disappeared in the part of the brain stem called the medulla — which means “eloquent” as it does so much, so beautifully. The brain stem is a signal box, and mine was working so badly that it might as well have been operated by Railtrack.

When you want your fingers to touch the face of the one you love, that desire has to go through the brain stem, which translates it into action. When you want those fingers to play the opening chords of Smoke on the Water, you still need to get through that signal box. And when you want to bend them into a fist and punch an Antipodean male nurse you still need brain-stem permission, and suddenly it’s not forthcoming.

At Charing Cross they began a series of increasingly unpleasant investigations — among them inserting a tube into my groin, passing it up through my body and injecting photographic dye into my brain. Michele always suspected that the way to my brain began in that general area, but really . . .

No one said that I was going to die until it became obvious after a couple of months that I wouldn’t. Then they admitted that they had thought I would.

Over the next two weeks, during which time I saw 14 neurologists, signal after signal stopped signalling: arms, legs, voice, swallow, sight, bladder. Michele and I consoled ourselves with the fact that at least my heart and lungs worked.