A Norwich actress has spoken candidly about how autism and mental illness are connected, as she preapres to appear in a TV show where she plays a woman with issues similar to her own.

Joanna Swan, 41, said she first realised things were different when she started school in west Norfolk in the 1980s.

But although her parents knew she had been identified as a gifted child, they did not know she had Asperger's Syndrome.

'I did not learn in the same way, I did not play in the same way, I did not talk in the same way,' said Joanna, who could read at the level of a 16-year-old while she was still at primary school.

'What nobody knew was that while I may have been gifted, far more to the point was I had, and still have, a condition called Asperger's Syndrome, which is a form of autism,' Joanna said.

'It's not easy to spot in girls and when I was growing up it wasn't even considered a possibility. I finally got my diagnosis from a top female expert in Cambridge, in 2013.

'By then I was 37, with a string of abandoned career paths and failed relationships behind me. My whole life up until then had been a series of attempts to fit a square peg into various round holes.'

Autism itself is not a mental illness, it is a lifelong neurological condition. But Joanna said where autism meets mental illness is in the stresses and strains of trying to exist in a world geared towards neurotypical people - the bright lights, the noises, the social conventions, the pressure to fit in.

'In 2002, while training to be a teacher I received my first diagnosis of mild depression. It didn't feel'mild to me. I was sad - desperately sad - and anxious, and hopeless and frightened of facing each new day.

'However, I also had enough of a guilt complex to prevent me from seriously contemplating or discussing any thoughts of suicide, so mild it was.

'I abandoned the teaching career and went back to office work thinking that for all my difficulties with office politics, it was the less stressful option. For the next 11 years I would be periodically on and off antidepressants, referred by the NHS for group courses in anger management and anxiety management, and by the occupational health department at work for individual counselling.'

Joanna said that by 2011, she began her journey towards an Asperger's diagnosis.

'The road to diagnosis was long and frustrating, and involved delving into a painful past not only for myself, but for my parents who also had to be interviewed extensively about my early childhood,' she said.

But since receiving a diagnosis, the self blame Joanna had felt for not fitting in and not feeling more mentally well had dulled.

'I know that if self-help techniques are not working that may be due to the fact that my brain is wired in a different way to the 'normal' brains they were developed to help,' she said.

'And I need to try something else, not beat myself up about it. I have found a sympathetic life partner and have kept and maintained a core of friends I can trust to be supportive. As a actress I'm working in an area where I can play to my strengths and have some freedom to plan and pace my work schedule so it doesn't overwhelm me.'

But Joanna said she was still battling with her demons.

'Unlike the classically depressed, I don't have long periods of deep depression, but find my moods change far more frequently,' she said.

'A happy, productive day can be followed by a day of quite profound despair, and vice versa. I no longer take anti-depressants because frankly I never found they made any difference.

'When I was taking them I was just as prone to negative thinking, ennui and self-loathing as I am without them. That's probably because they're for clinical depression rather than the sort of depression that comes with being an autistic person trying to make their way in a normal person's world.'

Joanna said yoga had helped her cope - although it was sometimes difficult to motivate herself to do it.

'I find I'm a super-woman when I have something I must achieve - a performance, an audition piece, a voice over or vocal recording - but as soon as that's done I collapse in exhaustion and it can take days to recover, especially if there was an element of meeting new people involved,' she said.

'I try to put my knowledge of autism and mental illness to good use. I work regularly as a role player with medical students and I'm able to give quite authentic performances because I've lived through a lot of this stuff.

'Performing is what I do best and when I do it to the best of my ability I'm able to feel proud of myself and grateful for my gifts, but there are costs. Many if not most actors can be vulnerable to depression when the work isn't coming in, but I also have to be mindful of my mental health when I'm working because of my anxieties and my various physical and emotional hypersensitivities.

'I filmed my first TV appearance earlier this year - I will be in an episode of Doctors on September 15 - having been hired via my casting agency VisABLE People, an agency representing disabled actors, to play a woman with issues similar to my own.

'It was the first time in my life I'd been able to approach a job, acting or otherwise, being totally open about my condition from the outset. It came at a pivotal time for me, because at the end of March, just before my agency sent me the casting details I was in such a bad way that I asked my partner to find out whether it was still possible to voluntarily commit oneself to mental hospital. Filming Doctors was one of the best things I've ever done. If I'd given in to depression or anxiety and not gone to the casting, I'd never have had that moment.

'I've had terrible days with depression since, too, and when that happens I have to keep reminding myself to keep going, because my fortunes could turn again, just as they did that time, and if I don't stick around I won't get to watch my episode, and I won't get to have other opportunities, either. I have to keep plugging away and finding reasons to hope.'

Joanna said her best tip was to use online exercise classes if it was too overwhelming to leave the house.

'I am a massive fan of Yoga With Adriene,' she said. 'She has hundreds of free classes on Youtube, at all levels including very gentle classes aimed at dealing with sadness, anxiety and depression.'

• For more from the EDP's mental health takeover special edition, click here.