‘You never think it’s going to happen to you.” Oh, that trope you find so often in the testimonies of the seriously and terminally ill. It’s an idea I’ve internalised and reversed. I’m convinced that “it” happening is inevitable. It started with an MRI scan for a legitimate health scare. When, after weeks of gruelling waiting, the results came back clear, it didn’t matter. I’d already moved on to the next terrifying obsession.

I’ve lost all ability to rationalise. A headache? I must be about to have a seizure. Achy leg? Deep vein thrombosis, probably. Stomach ache? Call the ambulance, it must be appendicitis. Statistics mean little. One person in a million is still one very real person with a life and family, hopes and dreams. It could be me.

On good days, I see my irrationality. Young and fit, why would I have a heart attack? On bad days, I can’t believe I’m so blase. Why wouldn’t I?

I look at friends, twentysomethings travelling the world, with awe and envy. How brave of them to venture so far from a GP. I wonder if I’ll ever escape this cloud of fear, this crippling state of hyper-alert. I long to make peace with my body and its aches and pains. Instead, I’m terrified of it.

I seek constant reassurance. I need my parents and friends to tell me I’m fine, because I can’t do it myself. I need them to laugh it off; I need to see they’re not worried the way I am.

My main source of comfort is the life that surrounds me. I observe every adult face I see. Parents. Grandparents. Colleagues. Fellow commuters. At the swimming pool, I watch imperfect bodies move, function, survive. Most people make it into old age without being struck down. Why can’t I believe I will, too?

• Tell us what you’re really thinking at mind@theguardian.com