DISPLACED IN MULLINGAR:IT'S NOT THE scariest of witches that's keeping me awake at night, it's the ghost of missed opportunities and the sins of youth. I was at Macbethin Dublin recently, with a friend, and was deeply moved by the witch in the play; a wolf-eyed terror in black robes, pushing a rickety pram, from whence emerged a little voice, not gurgling with innocence, but croaking rhymes like a tired old woman.

To me, it felt as if the entire 20th century echoed in that little voice; as if all the dead were there in that pram, watched over by the merciless eye of Fate, the witch - beautifully portrayed by Olwen Fouéré.

My companion thought less of the proceedings and twice I had to elbow his ribs to keep him awake.

He explained later that he'd been up half the previous night: "Like a yoyo," he said, "To the toilet - like a yoyo."

I told him I was also suffering sleepless nights, though I don't blame the prostate. It's an annual problem, when the clocks go forward. I rise at 7am, which is in fact 6am, according to the winter clock.

And I go to bed at 11pm, which is really only 10pm, so I am awake for ages, squirming like a fly trying to die, and thinking about all the wrong things.

Thinking about the extrovert I used to be, when I was young, and happy; always dancing, and chatting in bars, and making jokes, and sitting up till five in the morning in a flat, on the Mall in Sligo, with a couple of girls who worked in the bank.

As the years went by, I became more introverted, less likely to express opinions, except at weddings, when I would stagger around the lobby of some hotel at four in the morning looking for sandwiches, and then take more drink, and use archaic chat-up lines with the unfortunate night staff from Riga, who, when they were not hoovering the carpet at the far end of the foyer, or mopping the toilets, were obliged to carry pints of Guinness and vodkas to those dishevelled guests, still on couches beside the glass doors.

As a young person, I was relaxed about touching things and kissing things. I was at one with my body and laughed spontaneously. But age is a long journey to the interior, and to the hidden heart of "me"; the fact is that getting there keeps me awake at night.

It's ironic how the mistakes of a lifetime - that jumble of disconnected or forgotten moments, as unimportant as a jar of beads on a shelf - have the ability to assemble themselves in the dark night, and gather into a necklace of unbearable meaning and suffocating significance.

In the middle of one such night last week, I suddenly remembered a particular song, often played in the years when I danced to showbands with PA systems louder than a 747. It was called American Pie. I heard it for the first time as I kissed a beautiful girl one night at the back of the sports centre. I liked her a lot. A week later, I went outside the tent at Lavy Carnival in a fierce wind and kissed her again. But, during the kiss, I was distracted by the showband pounding out that same song; a pulse in the air, a vibration on the canvas tent, like a swarm of Chinook choppers.

The girl wanted more than kisses. But I wasn't paying attention.

So who knows? If it wasn't for American Pie, my life might have unfolded differently.

Not paying attention is the great remorse; it's the kind of thing that kept Napoleon awake.

I didn't share any of this with my companion after Macbeth, who was kind enough to inquire as to the health of my prostate. I told him it was fine.

We went to an ATM on Dame Street but were afraid to use it. The queue was too long. We had just enough change to buy fish and chips in Burdock's, which were soggy, and pay for the car park.

We enjoyed the highway back to Mullingar in silence. It felt like somewhere in the US. Somewhere that was nowhere. The nomadic "me" emerged, and was soothed big time, by the pulse of many headlights flipping past; everyone going nowhere.

My companion drove but was edgy at each green light, as sporty saloons with blacked-out windows and new BMWs zoomed past us at twice our speed; young turks of the new century, as snug in the night, as babies be, in little prams.