“If you've ever wondered what it feels like to be in a washing machine (and haven't we all?), this is your chance to find out. We chuck thirty litres of water, a (very) close friend and you into a giant translucent Sphere, roll you off the top of a hill and voila! instant spin cycle!”

It was the fish that did it. Until the fish I had been troubled by no more than mild anxiety, a vague nervousness around people and a reluctance to travel that caused me to respond with relief and a degree of gratitude when John suggested I go freelance and work from home. I was particularly glad to cease the daily commute into the city: although from Streatham I could go by train, rather than have to take the Tube, the confinement in close quarters with strangers still took its toll on me and I usually reached work in a state of high nervous agitation, which would gradually dissipate during the day until the journey home abraded me all over again. By the time I got back at the end of the day, I was raw and exhausted, and most evenings was able to do no more than drink a cup of hot milk and go to bed. The morning after I left the agency, I woke at the usual time and, when I remembered that I didn't have to get up and make the journey into the city, found hot tears of relief streaming down my face.

A year or so on, however, I began to notice that images of captivity were having an effect on me – pictures of animals in zoos, those terrifying Amnesty and PETA mailings that slide through the door, even the pet shop hamsters in their cages, would cause my skin to start itching as if I was wearing it inside out, and my stomach to rock with nausea. As a result, I was already making a conscious effort to avoid the triggers, but it didn't occur to me that there would be anything to fear at the shopping centre.

John and I had planned to eat lunch at an open-fronted restaurant on the ground floor, where I could sit at an inconspicuous table with a clear view of the exits; but in order to reach it we had to cross the large open space that was always given over to a promotional display or exhibition of some kind. This time, it was for a mobile phone network whose advertising featured vivid goldfish, and which had set up a series of tall cylindrical glass tanks in the centre of the space, pillars of white light in which floated small clusters of tiny golden fish.

The familiar itch started as soon as I saw them, my scalp burning as if it was pulling itself from my head. I tried not to look, but John had stopped to talk to one of the pretty reps and I found my gaze irresistibly drawn sideways to the lucent fish inexplicably suspended in the aqueous light.

“Why aren't they swimming?” I wondered aloud.
“These are tank-reared fish,” said a rep, stepping around the pillar. He was very shiny, his hair slickly gelled, his suit and tie gleaming. “They're not interested in exploring. They're just waiting to be fed, really. You'll see wild fish pacing up and down like tigers in a cage if they're put in an tank, but these ones just ignore it: it's as if they're pretending it doesn't exist. What network are you with, madam?”

I couldn't take my eyes off the fish – the curvature of the glass magnified and distorted them and they seemed to be inflating, their fins fluttering like signals. I felt as if my skin was shrinking, constricting my chest so I couldn't breathe, stretching my face so my eyes popped and my tongue swelled. My vision contracted to a point, then expanded outwards in a numbing wave that swept me from my body, so that I saw rather than felt myself collapsing to my knees, mouth opening and closing as the rep bent to catch me, John rolling his eyes, the pretty girl he was talking to pulling out a mobile phone and calling an ambulance.

By the time the paramedics arrived, I was still gasping, struggling to pull in each burning breath, convinced that my heart was giving out, and expecting to black out any minute. Despite John's insistence that it was really just a big fuss over nothing, I was taken to the hospital where, after a few tests, a young doctor came to tell me very politely that I had suffered a panic attack and my GP would prescribe me some medication, but in the meantime I could get dressed and go home just as fast as I liked because there were critical patients stacked up waiting for the bed.

John was smug, pleased that he had been the one to see through my clearly attention-seeking behaviour; but rather than be irritated by the diagnosis, he was gratified by it.

“It just shows what I've been saying all along, Yaz, that you're better off at home. That way I always know where you are and I can make sure you're safe. See, you can stay in your own little bubble in the big scary world. You're plugged in like a caravan hook-up – your shopping comes to your door, your meetings are in virtual conference rooms, your friends are on the phone: you never have to go out again. I practically envy you...”

It's not a fear of fish that keeps me inside now: it's the fear of panicking again, a fear of fear. Last time it was fish, next time it could be something else – a dog on a lead, a baby in a pushchair – it obviously doesn't matter whether it's rational or not. The experience of physical and mental collapse in front of strangers has left me profoundly uncomfortable with the idea of Out, of anywhere I might find myself thus exposed and vulnerable; and my brain has applied chemical shackles to my body to ensure it doesn't happen again – hence the shortness of breath, the rolling nausea, the antic twitching and sweating the further from home I get.

My therapist takes a Cognitive Behavioural approach, the idea behind which is that changing behaviour can change mindset; in practical terms this usually means forcing the sufferer to experience their anxiety repeatedly until they 'get used to it'. It seemed wrong-headed to me at first - the mental malfunction creates the anxiety, not the other way around, so why treat the symptom instead of the cause? – but apparently this treatment has the best rates of success. And to be honest - although there's a fair amount of talking too, not to mention the calming medication which I am trying not to need too much - it's the 'exposure events' which make me feel that at least I am putting up a fight, rather than meekly submitting to the tyranny of fear. I may have needed Mumma to get home from from the pharmacist's last week, but I managed to make it all the way there on my own, and even to collect my prescription, before the walk home loomed too large and I was obliged to make the call; and thus the panting shame of my ignominious exit was leavened slightly by this small victory, a minor objective achieved.

It suits John for me to be tied to the house this way. He prefers me to be here when he gets home, ready with hot tea and a sympathetic ear, comforting but not challenging, like a soft pair of slippers. He likes to sit at the kitchen table while I cook dinner, itemising the various irritations and outrages of the day for me: which selfish colleague monopolised his lunch hour so that he barely had time to read the paper; which thick idiot failed to understand the assignment and held the whole class up; the Head's blatant favouritism when allocating supervisory duties. John teaches English at the local comprehensive school; while I still worked in the city I would seldom be home before him, and would often arrive back to find him petulant and aggrieved.

“I suppose you went out for a drink with those people you work with,” he would say, although I very rarely did, finding that a few drinks made the journey home ten times worse. “How could you, when you know that I'm sitting here waiting for you? What a fool I am, utterly devoted to you, and you don't even love me enough to get home on time once in a while.” I would have to soothe and reassure him, promising to try harder tomorrow; and for the next few days afterwards I would force myself to shoulder into a packed carriage at 5.30, and stand with other people's bodies pressing warmly against my breasts, my rear, instead of waiting for a less crowded train to come along.

I thought that once I stopped going out to work, he would become less possessive, less inclined to worry about how, and with whom, I spent my time in his absence; but the fact that I was for the most part alone seemed to intensify his suspicion. He would telephone me five times a day to make sure that I was in the house, and if I failed to answer the phone he would race home at the first opportunity – morning break, lunchtime, once even in the five minute 'travel time' between lessons – in a towering rage, demanding to know what I had been doing, to whom I had spoken, convinced that I was taking advantage of his absence to entertain one or multiple lovers.

The night before the incident at the shopping centre, we had been out to a nearby Italian restaurant to celebrate our ten-year wedding anniversary. He had been ebullient, convinced that he was finally going to be offered Head of Department, and ordered expensive wine and steaks. The waiter made a great show of pouring the wine, rolling and curling the bottle with a flourish as if to conserve every precious drop, winking and aiming his Italian-inflected chatter at me, while I smiled back, warmed by the candlelight and John's good mood.

When we got home, however, his mood changed abruptly from candlelit to interrogatory as though a switch had been flipped.

“Don't think for an instant that I was fooled by that little charade,” he said. “How many times have you been to that restaurant without me?”

“What...? Never, I swear, only with you!”

“Do you take me for a moron? Flashing your tits, fluttering your eyelashes, winking, for Christ's sake, how obvious can you get? The guy probably doesn't even fancy you, he just knows a sad, desperate slut when he sees one.”

I'd seen John in moods like this before, and knew that the only thing I could do was to let him rage himself out, to patiently deny the accusations until he talked himself round again. That evening, he called me slut, whore, pointless cockshack; he accused me of soliciting sex from strangers in the street; he described in detail the betrayals and perversions of which he believed me capable; he repeated again and again that I was nothing, worthless and ugly, until finally, at four in the morning, he acknowledged that the poor sap in the restaurant was actually paying him, John, a compliment on his good taste in women; and decided that he could be magnanimous and say no more about it. He rolled over in bed and fell asleep almost immediately, while I lay wrung out and shaking next to him, feeling like a rag he'd used to wipe shit from his shoe.

The panic attack the next day took the pressure off after that, though. Once it became clear that I was in no condition to be sneaking off setting up assignations with lovers, or even friends, John calmed down considerably, calling just once a day or sometimes not at all, rarely enquiring about how I'd spent my time.

Lately he's been coming home later from school, sometimes not getting back until ten or eleven; he says he has to work late, that there's an Ofsted inspection coming up, or exams, or some other excuse, but I think he may be meeting a woman. I know I should feel horror, panic even, at the idea, but the truth is I just feel glad that the weight of his gaze is turned elsewhere for now.