I stopped believing my old man about his back. That's when things started changing.

My old man is a retired engineer. Spent thirty-eight years bending steel for the railways. Doesn't talk about his body, doesn't complain about the weather, doesn't tell you he's tired even when he's the only one in the room not laughing.

Eighteen months ago I noticed he was getting up out of his armchair on the wrong angle. Then I noticed him holding the kitchen bench when he stood from the table. Then — the one that made me stop pretending I hadn't noticed — I dropped in to see him on a Sunday morning and watched him shuffle out of the bedroom holding the wall, in the way men of his generation only do when they have decided privately that there is no other way to walk.

I asked him. He said, "Bit stiff, mate." Same answer he has given me every Sunday for forty-five years.

Not believing him.

I did something I had never done with my dad before. I stopped believing him.

Not in a confrontational way. I just stopped accepting "bit stiff, mate" as a real answer. I went through the bathroom cabinet next time he was making us tea, and I counted the ibuprofen. He was going through about a packet a fortnight. I asked his GP, who I had known for thirty years, who said — carefully, the way doctors talk about other doctors' patients — that "your father has not consented to be examined for it but I would put a substantial bet on chronic lumbar disc degeneration with referred sciatic pain. He won't take painkillers stronger than ibuprofen. He won't do physio. He doesn't tell me when it's bad."

I asked the GP what would actually help.

He said: "Sleep. The single most useful thing for him would be to actually sleep through the night. He doesn't, and the inflammation feeds the pain, and the pain breaks the sleep, and you can put a pin in either end of that loop. Most people put it in the wrong end."

What I tried first.

I bought him a new pillow. He used it. He didn't say a word about it.

I bought him a heated mattress topper. He thanked me. He used it once.

I bought him a weighted blanket. He told me, gently, that it was "a bit much, son."

I gave up trying to give him things, because I had begun to realise the thing I was actually buying with each new gadget was the feeling of having tried. He was not getting any better. I was getting better at managing my own guilt about it.

The bloke at the bowls club.

The thing that changed it wasn't a study. Wasn't a doctor. Wasn't an article. It was a bloke at my dad's bowls club, who I'd never met, telling me at the bar one Saturday afternoon that he'd been "shocking with the back" for fifteen years and his daughter had bought him "one of those grounding sheets" twelve months earlier and he was now, in his words, "not the worst player but I'm awake the whole game."

I asked him three questions. He answered them. He said it cost less than a tank of diesel and that it had a ninety-night trial.

I went home, I read about it for two hours, I did the engineer's daughter version of due diligence: I read the science, I checked who made it, I checked what it was made of, I checked the warranty. The brand was a small Australian company called Premium Grounding. The thread is surgical stainless steel, woven through cotton. No electricity. No batteries. No app. The cord plugs into the earth pin of any wall socket and connects your body to the Earth's natural electrical charge while you sleep — the same charge a man's body touched every day, all day, for two hundred thousand years before we wore rubber soles and slept on synthetic foam.

I bought one. I did not tell him.

The lie I told my dad.

I told him I was changing his mattress topper because the heated one had stopped working. I told him to stay in the lounge with the football for thirty minutes while I sorted out his bed. I went in. I lifted the fitted sheet. I put the grounding sheet on the mattress. I plugged the cord into the earth pin of the wall socket beside his bed. I put the fitted sheet back. I went out and watched the second half with him and did not mention it.

You cannot see the sheet. You cannot feel it. The cord is barely visible behind the bedside table.

He did not notice anything for two days. On the third night I got a text at 7am that said: "Slept till six." That was it. No question mark. No emoji. No follow-up. Just three words from a man who had been waking at 4am for a decade.

Three weeks in.

He still has the back. He still walks like a man whose lumbar discs spent forty years carrying steel.

But he is getting up later. He is taking less ibuprofen — I have started counting the packets again, and the consumption has dropped to about a third of what it was. He laughed at his own joke in the lounge last Sunday. He drove to the farmers' market with me on a Saturday morning, which he had not done since the previous winter.

I told him about the sheet on day twenty-five. He looked at me for a long moment. Then he said: "What did you pay for it?" I told him. He said: "And the trial's how long?" I told him. He said: "Right then." That is the closest thing to a compliment my old man has ever given me about a present.

Why I am writing this.

Because there is a generation of men in their seventies right now who will not tell their kids how badly they are sleeping. They will not consent to the physio. They will not take the strong painkillers. They will go through a packet of ibuprofen a fortnight and say "bit stiff, mate" until the day they cannot get out of the chair anymore.

If you have one of those men in your life — your father, your father-in-law, your grandfather, the bloke down the street whose lights are on at 4am every morning — I would put a sheet under his bed without telling him and let it run for thirty days. He will tell you, eventually, in three words and no emoji.

"Slept till six." — my dad, day three.