Oh yes, a number of members of the forum have. (Not me, I was a standard presentation of Type 1 as a teenager.)
I should have mentioned that there are tests if you can persuade your doctors that there's a question over your diagnosis.
Yes, it is not uncommon for more mature Type 1s to be misdiagnosed as Type 2 because some clinicians are of the erroneous belief that Type 1 only develops in children and young adults, so if you develop diabetes later in life, they often just assume you are Type 2.
I am on humilin I and I have 18 units per day once in a morning.
Are these the GAD tests? Or are there different ones?
As I understand it, Humulin I is an intermediate basal type insulin and probably should be taken twice a day to get full coverage. It will not cover the food you eat, just the release of glucose from your liver, so if you take it in the morning, it is unlikely to be covering your liver output overnight, hence your levels being high when you wake up, nor will it be covering any of your meals unless the dose is deliberately a bit high to give some meal coverage. Either way, if your levels are too high then it needs adjustment, but ideally you should ask for a basal/bolus insulin regime, where you have a long acting basal insulin to cover liver output and a quick acting (I use the term loosely 🙄 ) to cover the food you eat and inject that before each meal. This usually means 4 or 5 injections of insulin a day and ideally you need to learn to carb count so that you can adjust the meal time insulin according to the carb content of the meal you are going to eat, but it gives you much better BG management and more flexibility in what and when you want to eat. If you are a Type 1 diabetic, then this basal bolus system is the standard insulin regime, but even if you are Type 2 and needing insulin, you can ask to use this system for better BG management. It does take a bit more thought and effort though, as you need to learn to calculate your own doses.
The two tests for Type 1 are the GAD antibody test and the C-peptide test. The first indicates if your immune system has developed antibodies to attack your insulin producing beta cells and the C-pep indicates how much insulin your own beta cells are still producing. The two tests together are important as either one can be inconclusive and even then they need to be considered in context with clinical presentation, so the tests should ideally be authorized and the results interpreted by an experienced diabetic consultant.
