Wake me when it's all over

I nodded off in a cinema the other day. It wasn't a complete descent into slumber, one of those drooling slumps from which you have to be aroused by a man with a bin bag clearing up popcorn boxes.

I nodded off in a cinema the other day. It wasn't a complete descent into slumber, one of those drooling slumps from which you have to be aroused by a man with a bin bag clearing up popcorn boxes. It was a much more familiar form of cinematic sleep - the kind of teetering between consciousness and coma which is terminated by your head snapping back and the dim realisation that what began in all good faith as a blink has somehow stretched into a cat-nap.

And looking at some of the early reviews of the film I was watching, it seems likely that I wasn't alone. Wong Kar Wai's 2046 - the object of much speculation on the film festival circuit for more than a year now - has had quite a few writers drowsily fumbling for similar descriptions. It is "woozy, dreamlike" says one, while another says "hazy, hypnotic", and yet another "befuddling".

These are, I think we can safely say, code words. Professional reviewers prefer not to admit that they have fallen asleep on the job, or even that they may have struggled to stay awake from time to time. So they write something about how the film "induces a trance-like state in the viewer" - a phrase that tactfully reconfigures their failure of scrutiny as the director's artistic success. I wasn't failing to pay attention to the film, the line implicitly argues, I was paying attention so well that I nearly lost consciousness.

But the experience did make me think about our common assumption that the more focused the concentration the better it is - or at least it did once I'd taken a few deep breaths of fresh air and downed a double-shot latte. The critics need the tactful euphemisms because, by and large, grogginess is assumed to reflect badly on everyone involved. Art works aren't meant to be soporific, and audiences aren't meant to go to sleep. What we're meant to do is watch with beady-eyed vigilance, alert to every nuance and detail.

And yet that theoretical expectation is hopelessly disconnected from most people's practical experience of art or, indeed, of paying attention to anything. It's true that we generally start out with good intentions - perky and upright, all ears and eyes. But it's rarely long before that ideal state gives way to something more humanly mixed. Your mind wanders off briefly, following the scent of some entirely private association, and then has to be tugged back to the matter in question. Or you find yourself off the leash entirely, discovering with a start that you have no idea of where the play or the film have been while you were away.

Cinema and theatre are unusually hazardous in this regard due to the fact that you're forced to sit still in the dark, a condition of employment that makes things particularly tricky for some practitioners. Indeed it was said of one notoriously narcoleptic London critic that if he used the word "stimulating" in his reviews all it meant was that he'd managed to stay awake until the interval.

Other art forms aren't exempt from problems, though, even those which require active participation. Obviously if you fall asleep reading a novel, the novel stops until you wake up again. But that doesn't mean that it's impossible to drift off while reading. Who hasn't had the experience of coming to at the bottom of a page and realising that nothing above it has actually impinged? Or of picking a book up after a break and discovering, only after 15 or 20 minutes reading, that you've actually "read" this bit before?

When Martin Amis published his novel Other People, he announced that his ideal reader would read the book twice. This was optimistic, to say the least, but it also candidly acknowledged a general truth about reading - that one form of attention will often drive out another. In the grip of a conventional narrative (and Other People was knowingly subtitled "A Mystery") we are impatient with local detail, which raises the paradox that you can end up reading a novel less attentively when it has you hooked than when it doesn't. Presumably Amis wanted both versions - a first read so that people could find out where they were going to, a second one so that they could appreciate the scenery along the way.

The scenery in 2046, by the way, is often ravishing, even if it eventually turns out that the route is circular and that there is no conventional destination. But I can't be sure, of course, because I may have missed a crucial road-sign during one of those brief fugues of inattentiveness. That's the real problem with unconsciousness - it disqualifies you from categorical verdict. I won't blame Wong Kar Wai for inducing the drowsiness, though, and I won't blame myself for succumbing to it. Some things are actually better seen through half-closed eyes.