It was at work where I noticed my first symptoms. I was a non-clinical team leader training matrons and sisters in the art of electronic rostering. My girls called me a workaholic. My brilliant memory, the thing I relied on most, started letting me down badly. Simple words failed me in meetings, the names of colleagues I’d worked with for years were suddenly a mystery. I used to take long runs by the river to unwind, but my brain stopped communicating with my legs and I started having falls. I knew somehow that things were not right, but when I finally went to the doctors it took a long time to get the diagnosis. Initially my symptoms were dismissed as age or stress related (I was 58), but I was persistent and knew how the system worked. When I finally received the diagnosis, in 2014, it was devastating but it was also, bizarrely, a relief. It finally put an end to all the uncertainties which meant I could now start planning my life with this new, unexpected label attached.

I was determined to choose a positive path. The very nature of my diagnosis signalled the loss of the old me – my memories, my tastes, my abilities, my plans I took for granted – but, more importantly, it signalled the birth of the new me, a new chance. Many find it hard to believe, but I feel I’ve gained more than I’ve lost.

I face life with dementia head-on, as though I’m playing a game of chess, waiting for my opponent to make their move, then trying to outmanoeuvre and outwit them. I now own a cat, Billy, which would never have been possible before dementia entered my world, because I used to be terrified of animals. I would cross the road if a cat appeared within 100 yards of me. Not now. Billy is my soul mate. I see him and I instantly feel happy and calm. Now Billy and I often sit and simply stare out over the orchard beyond, watching the birds and enjoying the silence.

So many wonderful opportunities have come my way since I’ve been diagnosed. I refer to them as “the advantages of dementia”. When I explain this to people, they may think I’ve totally lost the plot, but keeping in mind the positives that come out of this kind of diagnosis helps me cope.

I’m part of many committees and research groups, because that’s how I believe I can influence change. I talk all over the country in many different settings. I call all this my sudoku, exposing my brain to different conversations in different environments. It might not improve my condition, but it certainly slows the progression. My worst weeks are when my calendar is empty, as I know dementia will seep through the lack of activity and win the day. Keeping busy keeps the symptoms at bay.

But it’s not easy. People think I magically appear at events, unaware of the effort and planning that goes into getting anywhere. But I’m not going to stay at home hiding from life, giving into deterioration. The hours I’ve spent checking routes, printing instructions to follow, walking maps – both there and in reverse to get back to the station – the photos of venues and people so I recognise them when I get there and then, of course, the inevitable Plan Bs in case it all goes wrong. All my planning and safety precautions I keep stored in my pink file that goes with me everywhere. Before my diagnosis, I was renowned for being highly organised and that skill has certainly become my life-saver.

So many things have come my way since my diagnosis and I think it’s because it’s so rare to meet someone with the disease who is willing and able to talk about it. People are curious about what goes on inside me. Julianne Moore invited me to have a cup of tea before the premier of Still Alice (the film about a woman who develops early onset Alzheimer’s), which was surreal. Then I was a consultant for the cast of the UK premier of the stage version. I remember saying to Sharon Small, who played the lead, to remember that Alice is not ageing, she’s cognitively declining. This enabled her to think differently about her role: how she moved about the stage and paused for a minute to think before speaking. I made a short film for the BBC about living with dementia that has now been seen all over the world. Last year we made an updated film about how we all are three years on.

None of these wonderful opportunities would have entered the radar of the very private me pre-diagnosis – I’m not sure I would have had the courage and I certainly didn’t have a cause. But after I was diagnosed, I became so shocked at the lack of awareness from both the public and clinicians that I now shout from the rooftops. I’ve become a new person, more brave and socially minded than I ever was before, and the gifts these newfound characteristics have brought me are immense.

I’m fortunate. I can type words far quicker than I can think and speak them – that part of my brain remains intact, thankfully. The part of my brain that controls written eloquence and imagination has remained, while I find it much harder to speak. Another trick of dementia I’ve learned to outwit. Writing doesn’t “improve” my dementia, but it helps me retain a sense of normality. It’s where I store my memories and if I stopped typing for any length of time, I would simply forget.

I didn’t even know what an iPad was before dementia. If I didn’t record events in real time through typing, my memories and experiences would have disappeared, each frame of the day fading into the unknown as another takes its place. People with dementia can remember feelings. We never lose our emotions because they’re held in another part of this complex brain of ours. When you come to visit us, we might not remember what we did during the visit, but we’ll remember how we felt after you left.

My daughters and I talk much more now than we used to. We discovered the importance of talking very early on post-diagnosis. After all, how do they know what I’m struggling with and how do I know what’s worrying them if we don’t talk? I’m still a mum and still want to help them, but I realise now that I’m more dependent on them. One thing I hope my book shows is how relationships change in a crisis, how new friends are made and how adapting to this new world is the key to surviving.

Technology used to be a mystery to me, but dementia has taught me to embrace its potential to help me cope with day-to-day living. I set reminders throughout the day to help me remember how to do the things I’d otherwise forget and they ding throughout the day. My new-found friend is Alexa, which sits next to my bed. If I wake and I’m discombobulated, I ask Alexa what day and time it is. If I’m anxious, I ask her to play me some calming music. In the evening, it’s Alexa who reminds me to take my evening medication as all the rest are taken in the morning. Whether I’m in the house or not, the message still appears on my phone and iPad. My daughters can now “track” me, so I’ll often get a text when I’m somewhere asking if I’m supposed to be there.

Throughout all of this – the symptoms, the diagnosis, having to create a new life for myself – I’ve learned that the type of diagnosis is irrelevant. It doesn’t even have to be a medical diagnosis like mine, it could be a divorce, a death, a birth. Every day we make decisions about the ways we live our lives, and that decision – be it small or large – can be the difference between what makes you and what breaks you when faced with the challenges that come our way.

I suppose the biggest thing dementia has taught me is to never give up on myself. Others may consider someone with dementia a “has been”, but we all had talents before diagnosis and we don’t lose them overnight. We simply need support from those around us to continue doing the things we love or to discover new talents within ourselves.

Dementia may be terminal, but then so is life. What I’ve learned living with dementia is, don’t dwell on the losses and don’t dwell on the future as you have no control over either. Instead, grasp every opportunity that comes your way and most of all enjoy the moment, because in no time at all that moment will be the past.

Somebody I Used to Know by Wendy Mitchell is published by Bloomsbury at £8.99, or £7.91 at guardianbookshop.com. World Alzheimer’s Day is 21 September