This was the moment that led the 43-year-old, from Robroyston, Glasgow, to take the steps to shed eight stones in less than a year.
Tipping the scales at 22st 4lbs at his heaviest, John was borderline diabetic and was being monitored for high blood pressure.
He also suffered from headaches and had been diagnosed with asthma and sleep apnoea, where sufferers stop breathing while they are asleep.
He said: "I wasn't one of these people who walked 10ft and had a break, but sometimes at night time or when I was lying down, I had problems.
"When I got diagnosed with sleep apnoea, I had a mask which was pumping air into me to help me breathe."
At various times in his life, John has tried to lose weight by dieting, but found it hard to keep the pounds off.
He added: "I've tried all the different things and three times in my life I've lost significant amounts of weight.
"But I find it really easy to dip back into old routines and before you know it you've put it all back on and probably more.
"The last time I lost quite a bit was 10 years ago when I got married. I lost about six stone with the Atkins diet and that's quite restrictive but as soon as you come back off that, you put it all back on again."
John blamed his most recent weight gain on a diffi-cult period in his work life.
He said: "I was made redundant two years ago and I had some health issues in relation to this as well, so I was under a lot of stress. I was a comfort-eater and it got to the point where I would eat things and hide the boxes from my wife just from embarrassment.
"Quite a lot of my adult life I've done that."
But he got another job and is now a support worker for young adults leaving secure facilities.
That gave him the positive attitude to tackle his weight issue and he knew it was important to shift the pounds and keep them off for the sake of five-year-old Erica and his wife, Katie.
John has also ditched the inhalers and the oxygen mask for his sleep apnoea, because he now feels he doesn't need them.
He said: "I think it's because I'm not just doing it for myself now, I'm doing it for my family.
"I want a better quality of life. It's the age-old thing, you want to be there to walk your daughter down the aisle, as opposed to her not having someone there."
Joining Weightwatchers in October last year, he found their points system easy to deal with and instrumental in helping him maintain his slimmer size, which now sits at 14st 4lbs.
He said: "When you go for your first weigh-in, it's slightly embarrassing, but everybody's there for the same reason and it's all about losing weight and maintaining weight.
"I have a very supportive team leader, Fiona Dickson, who has been brilliant, and I just do what works for me.
"I think a lot of people see Weightwatchers as a female thing, but I took to it well and I think anyone else could make that step."
As well as taking part in classes, which he now goes to once a month to help keep the pounds off, John has also found a new interest in exercise.
He added: "I've got weights. I've not joined a gym because I've joined gyms in the past and I thought it was a waste of money for me.
"I've got a cycling machine. I've been out walking and got some Apps on my mobile phone telling me how many calories I've burned and how far I've walked.
"I don't do it every day a week, but if I don't do anything for two days I get a wee bit agitated and I miss it. If you'd asked my family and my friends, they would have said I was never that type of person before.
"So all these things are about being here for my family and making myself a positive role model for my daughter as well because she's at that age where she's starting to question these things. She sees that I've lost weight and am exercising, and she wants to join in."
Katie thinks what has worked for John has been his total lifestyle overhaul.
The 37-year-old said: "This time I think something clicked. He needed to have the structure of a class and that support there.
"It's not just about a diet as a quick-fix, this is for the rest of his life.
"I think there's been a real shift, because we've always tried not to talk about being fat, for the benefit of our daughter it's being fit.
"He's just so much more upbeat and positive and I think he's done fantastically."