A 176-kilogram Christchurch man who had to be lifted back into his bed by four firefighters knows he may not live to his 75th birthday.

Wainoni resident and diabetic Raymond Macaree, 69, was rescued by the Fire Service about 2am on Monday after his blood-sugar level suddenly dropped.

While trying to reach for something sweet on a nearby tray, he fell out of bed and could not get back up.

"I was getting cramps and couldn't move my leg properly. I started sliding into a diabetic coma and kept trying to wake myself up, but it was getting more difficult."

He used his medic alarm to alert two St John paramedics. They tried to force their way into his home but could not get in.

They then called the Fire Service, and firefighters managed to get inside and unlock the door so Macaree could be treated with a glucose injection. Four firefighters then worked together to lift him back into his bed.

"I'm really, really grateful to the Fire Service, they did a magnificent job," he said.

Macaree did not know why his blood-sugar levels had suddenly dropped, and said he was careful to manage his diabetes.

"It's more or less a juggling act, but I've been doing it for 30-odd years."

He said he had been overweight "all my life", getting bigger after he retired. "I was down to 120kg when I was working but that was pretty heavy work, so now I've retired it's gone up, and the insulin doesn't help my weight either."

He was able to move around his house with a walking aid and used a bus, taxi or had his family help if he needed to get somewhere.

Helpers from Nurse Maude came in five times a week to help shower him and twice weekly for housekeeping. He bought his groceries online.

Macaree said he had tried many times to lose weight, but had never been successful. Health problems caused by his weight and diabetes meant he was unlikely to make it to his 75th birthday, he said.

- © Fairfax NZ News