Wendy was just 58 when she was diagnosed with early onset Alzheimer's. This is how doctors knew.

The following is an extract from ‘Somebody I Used to Know’ by Wendy Mitchell (with Anna Wharton).

I’m sitting in front of Jo again as she tells me the three words she wants me to remember by the end of the session. She starts going through the same memory tests as she did six months ago. When she asks me to name objects beginning with a certain letter, nothing comes. I glance around the room for inspiration, my eyes flicking back to hers, noticing how she watches me, how she knows I’m cheating.

“Take your time,” she says gently.

Eventually I find a pen, a pad, a pencil.

“OK,” she says, writing them down.

It’s obvious to both of us that there has been a decline, and yet Jo’s gentle, confident manner distracts from the fear that’s gathering in the pit of my stomach. She leans across the desk and hands me a piece of paper and a pen.

“Can you draw a clock for me?” she says.

Easy, I think, and yet when I lean forward, the pen hovers above the paper; the circle isn’t quite what I remember a circle looking like. I start filling in the numbers, my brow furrowed in concentration, but it doesn’t look right – the twelve is in the wrong place. I sit back and stare at the page. Why is there no room for the twelve?

“I’m sorry,” I say. “It’s so strange. It’s just a clock.”

“It’s OK,” she says, making another scribble inside her notes. And then she asks for those three words she’d told me at the beginning of the session, and again, they’ve slipped away without me noticing. “We’ve got two more weeks to go, Wendy,” she smiles, closing my file. “Plenty of time to try again.”

The third and final set of test days dawns and I’m back in front of Jo as we go through similar tests and this time, it’s just the same. At the end of our session, she sits back in her chair.

“How do you think that went?” she says.

“I know it didn’t go well,” I venture. I pause for a second, enough time to muster up the question I’ve wanted to ask for so many months. “What do you think it could be?” I say finally.

She looks into my eyes, and her voice is calm and steady. “Possibly dementia, but I can’t be completely sure, not until we get the results of all the tests.”

“Of course,” I reply. But I’m not sure how the words reach my mouth because a numbness embraces me, and a sadness too, a feeling that this is the end because that’s all I know about dementia; the blank stares, the helplessness, the confusion. And everything I’d been determined to avoid since I first saw whispers of the word in the letters that went between Jo and my neurologist.

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Back at home, I sit down in front of my computer, open YouTube, and slowly type in the letters, my finger hovering over the return key before I search for ‘dementia’, daring myself perhaps, unsure if I’m ready to see the results. The videos that appear on screen are exactly the images that my mind has been conjuring up since Jo uttered the words; men and women at the ends of their lives, old and white-haired, blankness written large across every face, confined to hospital beds. Surely she must have got it wrong? None of these people are like me.

My eyes skip through those videos, searching for something else, something more relatable and at the same time hoping that anything like me doesn’t appear, and that’s when I find Keith Oliver.

When the video starts, I’m relieved to see an intelligent man similar in age to me, sitting in a chair at home, his backdrop a beautiful green garden, speaking lucidly and eloquently into camera. As he starts to tell his story – how he was the headteacher of a busy Canterbury school, how two years before the recording he started to have unexpected falls, a feeling of fatigue, of just feeling ‘unwell’ – I am transfixed. I watch more in utter silence, mesmerised how, like me, he’d started to struggle at work with simple tasks like meeting deadlines, retrieving and recalling information, using the phone, multitasking. The more I watch, the more it makes sense, and yet the recognition is no longer frightening.

Instead, a feeling of relief is creeping over me. He likens having dementia to the weather; some days are sunny, but on others the clouds gather. ‘When it’s a sunny day, I can hold a conversation with very little difficulty,’ he explains. ‘On a foggy day, finding those words is a real challenge.’

I think back to all the days at work when I’ve felt isolated in conversations, finding it impossible to retrieve the right words to join in or keep up. Keith has experienced exactly the same thing. His story was so positive: he talked about how he felt that his health had maintained a good level since his diagnosis thanks to his determination to live life to the full and focus on the things he enjoyed.

By the time the eight-minute clip has come to an end, life really doesn’t seem as bleak. The ideas I had about what a person with dementia looks and sounds like have been challenged.

Keith looks so normal, and I must look no different; he still does the things he enjoys, and so I could, too. It’s not so much mortality that hits me full on, but that sense of time – or, rather, lack of it. That’s what dementia steals, the future you imagined all laid out in front of you, with no idea when something more final might come.

Somebody I Used to Know by Wendy Mitchell (with Anna Wharton) is published by Bloomsbury ($24.99). Out now.