The onset was fast. It was December 2003 and the midnight screech of police sirens, usually no more than irritating, suddenly seemed deafening and unbearable. Sleepless and paranoid, I would wander the house at 3am seeking spy equipment. In the daytime, flickering TVs and "wrong number" callers to my mobile, things others would hardly register, seemed to signal imminent danger. And hovering helicopters zoomed in on my every move with sophisticated zoom-lens technology.

At the time, I believed that I was at the centre of a conspiracy populated by a quasi terrorist gang of scriptwriters, songwriters and presenters who communicated with me via the TV, radio and computers. This group of people, who I believed lived in London art squats, wanted me to suffer excruciating, lifelong physical pain in prison.

After six weeks of terror, no sleep and exasperatedly trying to explain my conspiracy theory to anyone who would listen – including Stafford Police – my mother took me to the GP. "Your thoughts aren't quite right, Erica," the GP explained calmly.

I protested: "But I'm sure these people are out to get me ... I can provide evidence!"

"I think we should get you in with a psychiatrist as soon as possible." I thought he was a total idiot for having no interest in what I thought was revolutionary criminal activity from the heart of London's art squats and my feelings of terror remained as they had been for weeks beforehand.

A few days later I had a consultation with a psychiatrist. This was at St George's Hospital in Stafford, otherwise mercilessly dubbed by locals as the Nut House, generally regarded as a place populated by the pitiful. We agreed I should try a medication called Amisulpride, an anti-psychotic, on a daily basis. But I remained convinced that these squatters were after me despite the psychiatrist, Dr Srinivasan, referring to my theory as a "false belief".

Still, I responded well to the medication and stabilised quickly. But it wasn't until much later that I was diagnosed with "paranoid psychosis". At the time I wondered if had schizophrenia, as that's what the tablet's leaflet says it helps. It was all a little confusing. Nevertheless my family were relieved that I was getting help and I generally didn't mention it to friends, partly because I believed that were involved in the conspiracy, too. While I could rationalise that they weren't, I could also rationalise how offensive it might be to mention how I thought they were trying to do me over.

I now know psychosis is not a condition in itself, but a symptom. Around one in 200 people will have a psychotic episode at some point, and may find it hard to distinguish between what is real and what is imagined, sometimes seeing or hearing things that are not there. Sufferers are often terrified, so the fear they inspire in others seems ironic.

The worst reaction came from my employers. Shortly after seeking help and seeing the psychiatrist, but before the medication had taken full effect, I broke down in the office reception. A man had come in to fix the office fax machine but I believed he was installing spy equipment into it, to monitor me. I cried and spoke of my conspiracy theory (which apparently translated to them as gibberish) for about 10 minutes before calming down. Then I took two days off before returning to work. The following week, I mentioned I had a doctor's appointment, but omitted to mention that it was a follow-up with a psychiatrist. However, my boss enquired: "Is this to do with what happened the other day?" And I said, "Yes."

Very shortly afterwards I was called to a meeting with my boss and the office manager and they said what had happened meant I couldn't do the job. There was too much risk it might happen again. I was speechless for all but a few minutes before being shown the back door "to save any embarrassment". While they outlined my right to appeal, I was in no state for an employment battle and felt ashamed anyway. Despite the fact that I was quickly stabilising on medication at this point, the impact of such treatment led me to contemplate suicide. The terror had subsided and I was left feeling hopeless and desperate. If I wasn't part of a plot, then I was insane. It felt like a lose-lose situation in which I'd be locked-up either way. And I'd lost my job. I couldn't see a way out but I had all these pills to hand.

As luck would have it, I received three text messages from friends as I stared at a handful of pills under the duvet. It was enough to put the pills down and put the kettle on to mull things over. Days later I drastically decided to move to New York – to run away. I'd lived there briefly before and found it a great place to dissolve into. My life was a mess, I'd had a trauma and I needed to turn the page and bugger off for a bit.

Before departing to the States I remember peering over a nurses shoulder at my medical notes as I was getting undressed for a smear. "Psychotic". There it was. It was a frightening word. Even I was afraid of me and what that meant I'd do. And although I was stabilised by this point, I still feared prison as much as I feared being sectioned. I immediately decided not to have children, because I might murder them. It took a long time for me to realise that I wasn't a threat to other people. So it doesn't surprise me that anti-stigma campaign Time to Change found that 44 per cent of people in the UK believe people with a mental health diagnosis are potentially violent. If that's the case, what good is a diagnosis? My official one is "paranoid psychosis", but various psychiatrists have suggested I use "nervous disorder" or even the slightly odd "acute disability" when I raise it with potential employers. According to Mind, more than half of people would not employ the person they thought was the best candidate during an interview if they had disclosed a mental health problem.

The general consensus is that I got sick through a combination of stress and smoking skunk (something I was doing to quell the stress, ironically). However, since 2003 I've been taking medication, thus successfully managing my psychosis without too much problem, while also trying to talk frankly about it through my writing. However, stigma still looms. Since returning from New York, I've experienced ostracism and many a frosty reception from groups and individuals while working in PR, retail and moonlighting as a journalist. Rebuffs like this are mostly the result of slightly eccentric ideas I share with colleagues without thinking them through. I often feel anxious around people, which sometimes makes me act in haste. I'm so sensitive to these results and they only compound my paranoid thoughts that people are out to get me. It's upsetting. So much so that today I work from home as a freelance journalist and content writer in order to avoid other people as much as possible.

Before going freelance full-time late last year, writing online content and articles, I was teaching at a university and some of my students at the time started a link on Facebook which ridiculed the paranoid symptoms I'd shared in a newspaper interview that was still on the internet. The comments were really unpleasant. It was a rude awakening and I concur that the worst part of my so-called mental illness is what society thinks it means. People too often forget that there's a difference between mad and bad. During my meltdown in December 2003, I didn't squash a fly. Nor did I go on a murder spree, blow up any buildings or run around naked with a banana up my bottom causing a public nuisance. A friend with a diagnosis of bipolar illness sometimes holds the belief that she's a Hindu god. How many Hindu Gods would act in an aggressive way? It might be the response of a sane person to get the facts before passing judgement or forming opinion.

According to Mind, it's a fact that there's more chance of being killed by lightning than by someone with a mental illness. Compared with all killings, the number committed by people with mental health problems has actually fallen to a little more than 1 in 10 (and only a fraction of these are attacks by random strangers). Arguably, more people will experience psychotic symptoms without ever receiving a diagnosis of a mental health problem, too.

So does my diagnosis mean I'm mad? No more than you are, I think. So long as it's managed with medication I'm okay and not overwhelmingly, or astoundingly, paranoid or psychotic. I have a small circle of close friends that are the best in the world. I work independently and have even started my own fashion label, Medfed, which is colourful and fun. It aims to challenge the bleak mental health stereotypes that are often in the media. In groups and with individuals, I'm still a little awkward, even angry sometimes. I get overly nervous, sweaty or excited around new, loud, terribly clever or attractive people. Tories tend to scare me somewhat, too. But this is surely the response of a sane person.

Mental illness – how to help

* One in four adults will experience a mental health problem at some point in their life and 87 per cent of people with mental health problems reported the negative impact of stigma and discrimination on their lives, according to the Stigma Shout survey.

* If a friend or loved one is mentally ill, be there to talk and listen. Most mentally ill people report being afraid to talk about their problems, because they fear people's reactions. If someone talks to you, acknowledge their problem and let them know you're there for them.

* Be understanding and supportive. When people with mental health problems do speak up, the majority report being misunderstood by family members, ignored by friends and work colleagues, or called names and much worse by neighbours. Be sensitive to their situation and respect their feelings.

* Make time to stay in touch. Include them in your day-to-day activities, such as going shopping, going to the pub or taking a holiday.

* Ask how you can help. People may want support at different times and in different ways.

* Keep in mind that having a mental health problem is just one part of the person. People don't want to be defined by their mental illness.

The Time to Change campaign, run by the mental health charities Mind and Rethink, aims to end the stigma and discrimination faced by people with mental health problems. Go to Time-to-change.org.uk.