Mine is 3 years on Saturday!
I diagnosed myself with a BG meter I'd bought for myself a couple of years before, but never used.
I'd been feeling pretty ill all weekend, and been suffering with numb toes and recurrent thrush for about 6 months, and my mother in law had said it sounded like diabetes (obviously I didn't tell her about thrush). Wanting to prove her wrong I tested my BG for the first time...
I remember saying to my wife: "Well that's alright, my BG is 23 mmol/l, I don't have diabetes...", thinking that Diabetes was about too little glucose not too much. The penny dropped when she tested hers and scored a 5 mmol/L
And with that I had to go to a business meeting in Holland for a week (bizarrely in a hotel without internet). I spent the whole week in worried conversations to my wife was furiously researching diabetes on the internet.
She was the one who discovered low-carb, and together, we worked out what carbohydrates were. By the end of that week (apart from a small misunderstanding about the carbohydrate content of weetabix) I'd got my BG slowly down from 23 to under 10 mmol/l , and a few days after that down below 7mmol/l. I can still remember the feeling of absolute lucidity as my brain adjusted to non-hyperglycemic blood.
And that was it. I've never really been seriously hyperglycemic since.
It was scary at the time, but with the benefit of hindsight, it's one of the best things that ever happened to me. I think it saved my life.