If I had studied chaos theory before now I would never have made her get onto the couch at all. It is never wise to ask anyone to climb onto an object smaller than they are, particularly not one with a wobbly leg. I felt not to do so would be fattist. It turns out that to do so was in fact daftist. Now she has an appointment with the practice manager and I have a bruise the size of Bedford.

Mathematicians define chaos as a state of disorder, which fits exactly with the actuality of Monday morning emergency surgery. The defining features of chaotic systems are that, while complex, they rely upon a strict underlying order (and frankly the order that governs the NHS feels positively totalitarian), and that small variations can cause large changes.

So in chaos, nothing is truly predictable, apart from the fact that the future is unpredictable. This means we can't say that I was already doomed long before the moment when I was first trapped by Mrs Enormous' right leg then crushed against the carpet as the wobbly leg decided to fold, but we can say that the progression to disaster was predictably unpredictable.

We can also say that when a woman of Wagnerian construction wants an intimate examination, a GP the size of a stick insect should not be attempting it alone.

Government should learn from this. The consequences of the crashing couch are nothing compared with the consequences of enormous changes to that Leviathan system of predictably unpredictable chaos that is the NHS – for what more extraordinarily chaotic system is there?

Somehow it works, against the odds, probably because all the bits of chaos are endlessly corrected back into something resembling order by a mixture of goodwill, panic and sheer bloody-mindedness. Politicians tamper with the foundation stones of such a beast at their peril. Mr Lansley risks a crushing by an awful lot of thighs.