The trigger for me is overwork, or overdoing it in any way. For instance, last week, I worked a week of nights, then drove from Dublin to Connemara in the rush hour, taking seven-and-a-half hours in total. That night I got a raging migraine.

Immigran (on prescription) is the only thing that works when I have the migraine - as well as walking, to keep the pills down and keep the blood moving, and hot-then-tepid-then-hot showers. If it gets me fully before I get the Immigran, there's no hope, because one's digestion shuts down with a full-blown migraine, and the pill just sits there until vomited up.

But if I realise before I'm in the full throes, there's software called Pzizz (it's $60 but it's worth it) which generates auto-hypnosis snooze and sleep recordings. You put them on your iPod and play them over earphones, and they're really helpful for getting into a deep, relaxed sleep.

I think the problem with overtiredness may be that I get to sleep all right, but I'm so tense that I'm clenching my jaw and (the dentist tells me) grinding my teeth, and this puts the neck and jaw muscles into a rictus. Then I wake up with the start of the headache, but I'm so exhausted that I mutter "'Twill be better in the morning" and plunge back into an exhausted, tense sleep.

The tense muscles cause the veins leading up through the neck into the brain to tense, and voila! migraine.