He started off filming me doing simple exercise routines, and I’d chat as I did them, about anything that came into my head. Eating well, getting fit after illness, how to work out in crap weather.

The numbers were tiny at first but then they began to grow. The Americans seem to love my accent, the Brits my sarcasm. Dad’s camera angles and edits flatter me. I’ve developed a tough-love charm, taking the piss out of myself, sending the whole thing up.

Last night, though, I felt different. The fear was part of it. Plus, I decided to record it with my webcam, instead of asking Dad to do it. It felt more intimate.

I started off talking about why I needed it, and what defibrillation means, but soon I found myself going further than I’d planned to, talking to the camera as though there was only one person at the other end. Perhaps a boy or girl like I was, all those years ago, when I couldn’t decide whether to let them implant this machine in my body. I told my imaginary viewer how my life had been turned upside down by cardiac arrest. How many times the defib had shocked me back from the brink, even though to begin with I wasn’t sure I wanted it to . . .

And I found myself talking about deeper stuff. I confided in the unblinking webcam that I’d never known real fear till I had my son, and now the terror of leaving him was greater than I could have imagined.

‘This is my story, not his,’ I said. ‘He is entitled to his privacy so I won’t tell you any more about him except to say he’s taught me so much with his sweetness and his curiosity and even his insane small-boy rages.

‘Without him, I don’t think I’d ever have graduated, I’d never have been the best man at my best mate’s wedding, with my son as the page boy.

‘Honestly? I think he healed me. I was toxic before him. Full of self-pity, only ever thinking about poor me. But having a kid means you have to put them first.

‘And I am so glad I went through with having the box put in all those years ago because, without it, there would never have been him. It is the best thing that could have happened to me.’

‘Twelve thousand, three hundred followers now,’ my mum tells me.

Leo sits on the hospital chair, glued to his game of Super Mario on the Nintendo I bought for his sixth birthday. He seems completely unfazed by seeing me here. Which is a good thing, in case he ever needs treatment himself . . .

No. Don’t go there. He’s been fine so far.

So were you at his age.

‘I can literally see the subscribers going up when I refresh your channel on my iPhone,’ Mum says.