In my opinion, your father's personality change does not sound like it comes from diabetes. When out of control high or low, a person often does become grouchy, depressed, or sometimes completely irrational, but normally once the glucose levels are back to normal, the person behaves very normally. I wonder if you should ask his doctor to check for other conditions, including early onset Alzheimer's. My mother-in-law developed Alzheimer's at about this age, and the first and only symptom was depression. My father-in-law is developing the old-age version of dementia now and one very noticeable symptom is depression and the fact that he is more easily annoyed than he was before. New treatments can change this drastically for the better. But an evaluation should be done. If he is developing something like this, the sooner he starts on medications, the sooner he returns to the father you used to know.
As for hypoglycemic unawareness, this is NOT caused by "progression of the disease." It is something that can be fixed. Many diabetics lose their symptoms of hypoglycemia after repeated lows are not caught before the body's liver dumps emergency sugars into the system to try to save the person. Unfortunately, once this happens, it takes several days for these emergency sugars to completely be removed, and if another low happens before this, the brain does not sense that the body is low. So recent studies indicate that preventing ALL lows for a short period of time (studies seem to vary on exactly how long this takes, but some say as soon as 2 weeks) help the brain to recover its warning symptoms.
So it appears that your father is perhaps taking a bit too much insulin if he is having frequent lows. Please do talk to his physician, who can help him rethink his dosage and hopefully be free from hypoglycemia long enough to recover his warning symptoms.
If your father's lashing out is because he is perhaps frightened because of the hypoglycemic episodes, then once he recovers his warning symptoms, he should feel more in control of his life, and hopefully will be easier to live with.
Hello. Wow, do you have a lot on your plate. I'm not a medical professional, just a parent of a kid with diabetes. From your description of your father, it sounds like he's progressed from a functioning adult to someone completely dependent on others to simply remain alive. He almost assuredly has severe hypoglycemic unawareness, you don't say whether he's been diagnosed with that or not. It is when your body becomes less sensitive to lows over time, so you can't tell when you're going low. I am sure that his condition is incredibly frustrating and aggravating, and you see it exhibited in how he's lashing out at anyone and everyone. Again, I'm not a medical professional, but that's almost certainly what is going on.
Have you talked to his endocrinologist about his conditions? Together you might be able to come to a solution which might address the lows, which would give him some personal freedom back. I think that is your first step, try to find something which will help either prevent the lows or at least help address the unawareness. I don't know what your insurance situation is, but have you considered a continuous glocose sensor? It would be able to signal when the blood sugars are dropping and the person needs to act to prevent the low. Something like this technology would give him control over his own disease again. I'd bet that's what he really wants.
If you just need someone to talk to and vent to, I'd suggest that you contact JDRF's Online Diabetes Support Team. The link is here:
http://www.jdrf.org/index.cfm?page_id=103451
They might even have more ideas about how to help your dad. Good luck!