Ordinary people get them too: Atonia and splanchnic activity: Giles Smith on Oliver Sacks's classic study of the ultimate headache

Migraine: there's a lot of it about. Oliver Sacks's detailed study (Migraine, Picador, pounds 20) says that roughly one person in 10 suffers from 'common' migraines (a burst of intense head pain), and one in 50 endures the 'classical' type, in which a bout of sensory hallucinations performs a kind of curtain-raiser before the main headache comes on. The following effects clamour to be part of the show in both cases: fever, acute sensitivity to light, dizziness, nausea leading to vomiting, gastric disorder, irritability, chronic lethargy, diarrhoea, water retention, Uncle Tom Cobleigh and all.

Just don't call them headaches. We're in a totally different pain realm here from the dull and heavy throb of the conventional hang- over. Joan Didion, who was suffering a 'classical' migraine nearly every week in the 1960s, wrote in an essay in The White Album: 'That no one dies of migraine seems, to someone deep into an attack, an ambiguous blessing.' She was not exaggerating. Sometimes the pain is so acute it alters the sufferer's face for the duration of the migraine. Sacks notes, 'These changes may be so marked as to suggest the picture of surgical shock.' Try fending off that with an aspirin and a lie down.

Having read Sacks, I can confidently lump myself in with, not the commoners or the classicists, but a third category of sufferers, gifted with many of the usual symptoms, but at the same time treated to an additional gimmick. For five years I have suffered from what I can now call 'migrainous neuralgia'. It is, I am gratified to relate, 'a highly distinctive variant' on the traditional forms. There are periods of remission, lasting four or five months. But then come the attacks, in vicious clusters. It is as if someone has got their hand in behind your eye and is maliciously squeezing a bruise on your brain between their thumb and forefinger. And they do this for two hours or so, every other night for about three or four weeks.

Needless to say, the pain involved is big box office, Premier League stuff. 'Whereas the majority of migraine patients sit or lie down, or wish to do so,' writes Sacks, 'the sufferer from migrainous neuralgia tends to pace up and down in a fury, clutching the affected eye and groaning. I have even seen patients beat their heads against the wall during an attack.' Altogether it's . . . well, a real headache.

And there is, it would appear, no drug you can take to cure it. Nor is there any simple sense to be made of what brings an attack on, or why it stops. The really cute thing about migraines of all kinds is that they have no readily comprehensible cause - or at least the possible causes are so various and mutually exclusive from case-to-case that you're left baffled by the plot. Some people get them from over-doing it. But others get them from under-doing it (hence the phenomenon of the 'weekend headache' which hits people precisely when they stop working and start relaxing). So where do you begin?

This zone is ripe for Professor Sacks, the author of The Man Who Mistook his Wife for a Hat and Awakenings - someone who will always plump for the awkward singularity of the case history over smooth general theories. He's exactly the man to take a stand against the broad and doubtful notion that a certain kind of personality is somehow pre- disposed to migraines. Many writers in the field have evidently tried to tie this one up. Sacks quotes, with amazement, W C Alvarez, whose studies had somehow revealed to him, as recently as 1959, that a migrainous woman was more than likely to have 'a small trim body with firm breasts. Usually these women dress well and move quickly. 95 per cent had a quick, eager mind . . . Some 28 per cent were red-headed and many had luxuriant hair . . . These women age well . . .'

Sacks sinks this dodgy muddle- headedness by taking a sort of satirical poll of polls on the pre- dispositionists. 'The average migraineur is shown as a hypertensive perfectionist with one inverted nipple, multiple allergies, a background of motion-sickness, two fifths of a peptic ulcer, and a first cousin with epilepsy.'

But you can see why sufferers might be drawn to such fictions. In the absence of clear external causes, victims seek inside themselves for an explanatory narrative. Writing in 1968, Didion could say confidently, 'There certainly is 'a migraine personality' and that personality tends to be ambitious, inward, intolerant of error, rather rigidly organised, perfectionist.' Big of Joan to take all that on board about herself. Personally, I've always seen the 'migraine personality' in similar terms to Didion's, while linking it also to an elaborate humanitarian concern working in conjunction with an astonishing sexual prowess. But now that Sacks is in print, I'm going to have to ditch my theory. 'In short, migraine patients are as remarkable for their diversity as any other section of the population.' Sad to say, ordinary people get them, too.

According to Sacks, what is more likely than the existence of a 'migraine personality' is that your migraine has a personality. This is, in any case, from a therapeutic point of view, more worth dwelling on. 'Walking, at its most elementary, is a spinal reflex, but is elaborated at higher and higher levels until, finally, we can recognise a man by the way he walks, by his walk. Migraine, similarly, gathers identity from stage to stage, for it starts as a reflex, but can become a creation.'

Hence the common idea that migraines are the manifestation of displaced anxiety, which can be dispersed by resolving the worries. Again, though, it may not be so simple. Sacks also discusses the 'tactical value' of migraines for some patients, for whom they represent a self-preserving flight into illness. 'It is, paradoxically, not so easy to be well - it is easier in some ways to have a limited life, to be ill . . . One has now to learn to be well.'

Migraine was originally written in 1970, but was updated in 1992 and is now published in Britain for the first time. Much of it takes the tone and complexity of medical papers and the later sections read like a guide-book for physicians. But sufferers will take comfort in seeing their condition thought about with such clarity - no small achievement in a book which inevitably wields a lot of technical terms. Be alert for atonia, spontaneous ecchymoses, and undue splanchnic activity. And be ready at all times to submit yourself to electroencephalography. (There's a glossary at the back if you get into trouble.)