Harriet Walker: I think I'm dying, I tell my mum. 'You've had a coffee, haven't you?'

If this columns reads a bit jittery, that's because I've discovered coffee. Not in the Marco Polo sense; more that I've only recently taken my place among the rest of the adults and been able to stomach it.

For years, my experience of coffee was a Nescafé freeze-dried decaf – "Three sugars and enough milk to turn it the colour of the hide of a fawn," I used to instruct my dad as a teenager, while he poured and stirred and carried patiently (no, I don't deserve him).

I've spent my life going into Starbucks and ordering a hot milk with vanilla syrup or a soy decaf latte – an existential void of a drink, as one friend called it – because anything stronger would bring me out in a cold sweat. I'd vibrate around the place, get all sicky-feeling and anxious, then lapse into an exhausted fugue. "I think I'm dying," I'd call my mum to let her know. "I'm worried about everything I've ever done and ever will do, and I'm scared of that man over there."

"You've had a coffee, haven't you?" She'd ask, as patient as my dad. Then she'd talk me down. She's done it in person, on email, over the phone – once as I sat on the front row of a fashion show waiting for it to start.

It has been my custom to try out a coffee once or twice a year, just to see if I can handle it yet. And until recently, I'd invariably end up crying, slumped in a corner. A friend once had to usher me out of a gallery in Barcelona on hands and knees before I fainted in there; she refers to it as "that time you had an espresso".

I've found it terribly annoying, because I genuinely like the taste of coffee – when there's loads of sugar in it (what I really mean is I like the coffee-flavour Revels) – and I'm as keen as the next idiot to be part of anything known colloquially as a "culture" that handsome men with beards like to talk about.

On the plus side, I was pleased to have found a genuine trendy intolerance. Dairy makes me itch but I love cheese, so I ignore that. I lie on planes about having a nut allergy so they give me the delicious pretzels instead. I once made up an allergy to shellfish because I was too shame-faced to admit I have the palate of a toddler and don't know what to do with all the claws. I regularly tell people that fish shuts my airways so I don't have to feel awkward about leaving it when somebody cooks me one of the little swimmy buggers.

But, intriguingly, something has kicked in this year – call it weight gain or excessive fatigue, or having eye bags big enough to store two caramel macchiatos in (each), or even eating enough bread to mop up an entire reservoir of coffee. I'm suddenly able to withstand the effect of caffeine. Sure, the perspiration is dripping off me right now and I keep looking over my shoulder, but there's no angina this time.

So out with all the 'erbal teas and the decaf Tetley (oh, the mockery I've endured for that over the years), and in with Diet Cokes before bedtime, chocolate so dark it's practically savoury, and one of those yuppie coffee machines that wheezes and squeals like a randy asthmatic when you pull its levers. I haven't actually bought one of these, partly because I like presenting myself as a coffee ingénue, a weird and rare social specimen with no cafetière and no idea whether it tastes burnt or not. And partly because I have only one area of storage in my kitchen and it's currently taken up by a juicer the size of a tractor that I used once and have become bored with.

Still, it's all terribly exciting, drinking coffee, because I'm assuming a role in a new hyperactive, trendily running-on-empty tribe. Everyone knows this is the best tribe, otherwise why do so many people go and work in the City? My drink of choice used to be a chai latte that everyone used to wrinkle their noses at (I still say YUM to all the haters). That wasn't the drink of a clammy world-conqueror! Pah, a drink for librarians! Now I take a Samoan dynamite blend served super-wet with a side of angst. And I feel like Caesar must have done when he first realised Casca wasn't about to give him a hug.

Perhaps I don't quite know what I'm talking about when it comes to coffee. The thing is, I do actually like the taste of decaffeinated Nescafé in the morning. But now I know I could just as easily have a flat white instead, I feel more myself, more of a social animal. Whatever: I just feel cooler.