I’m just six weeks away from a brief holiday in warmer climes, and the cushion – nay, small armchair – of fat around my midriff shows no signs of melting in the spring weather.

Which means, if I’m going to cram into any of last summer’s clothes, I’m going to have to lose well over a stone before I go. A perfectly feasibly task, as long as it includes contracting a wasting disease or undergoing surgery.

Or, says my helpful husband, you could just eat less and do some exercise.

Oh, right, I say. If there’s one thing that’s irritating, it’s listening to dietary advice from someone who knows nothing about losing weight whatsoever. He has weighed roughly the same for about 20 years, whereas over those same two decades I have swung from a 14 to a 10 to a 16 and a bit, several times over. So I know exactly how to take control of my BMI, thanks very much.

When I next get out of the bath, though, it dawns on me that my body is now less like a temple and more like a statue of a fat little Buddha. Something in my brain suddenly clicks – it could be a blood sugar surge – and that’s it. I am now in the right frame of mind to divest my mortal coil of excess fat.

I put on sensible shoes and set off for a brisk walk. As long as you stay on the flat, brisk walking isn’t too bad, and before I know it – well, after half an hour or so – I’m in the town centre, and countering the tedium of perambulation with a little window shopping. Two hours later, I’m back in the house, and after a few minutes on the sofa am able to breathe properly again. I walked miles, I finally manage to blurt out.

My husband, who has just been messing around gardening and building things while I’ve been out doing walking, shows me how to measure how far I actually went, courtesy of the internet. It was just over five miles, which is good enough, but when I convert it to kilometres it’s 8.78. That IS miles.

For a moment I forget my shaking legs and the nausea and smile to myself. If I don’t have any dinner tonight, I’m on the way to those white shorts and halter neck top.

Next day, I decide to take a different route. It’s a figure of eight, out towards some larger shops.

Take some water and a raincoat, says my husband, but I don’t bother with a coat because the weather actually looks fine. In fact, it’s unseasonably warm, I think to myself as I struggle back to the house for the water I left on the table. I sit down and swig half a litre, and that little Buddha seems to have got into my head, for I can hear a voice telling me that’s enough walking for one day.

Don’t try that, I reply, and leap up, grab a rucksack and head off by the country path to Sainsbury’s. It’s amazing when you go places by car how short the journey seems. I am reflecting on that as the large orange building in the distance doesn’t seem to get any nearer, however fast I walk. It’s like the moon. Several light years later I stagger into the store, all feeling below the thighs now just a distant memory. Except for blisters on my heels.

On the way back, I feel the rucksack getting so heavy, that I turn round to check that a small child hasn’t got caught up in it at the check out. Dumping some ballast has to be an option. I consider what I could do without tonight. How will it look if I go up to a stranger on an isolated lane and offer him a free bottle of pinot grigio? It could seem odd. My only other strategy is to ring my husband and cadge a lift – or phone 999. This does feel like an emergency, after all.

Think of marathon runners. Think of Scott of the Antarctic, I tell myself. Did he call an ambulance? No. Though perhaps… no, don’t go there.

And it works. Before you can say the word collapse, I am crashed out on the bottom step of our staircase, having overbalanced with the rucksack. My husband is deeply concerned.

That was 11.985 kilometres, he reads out. I can’t speak.

Not because I’m overcome by my achievement. I just can’t speak.