I agree that if blood sugar is out of the normal range, moods can be off, too. I have never personally noticed my mood changing if I am high, but I tend to have more lows than highs. If low, I notice feelings of anxiety, depression, or irritability. As WAK has noted, this is easily checked by doing a blood test if you notice that you are feeling upset. If low or high, try to adjust. Then notice if you feel calmoer in about 15 minutes, and keep track of these moods. Do discuss with your endocrinologist.
I am not a physician, but the mom of a type one diabetic and the daughter of a type diabetic. I can tell you that when my daughter blood sugars are too high or too low she has mood changes. When her blood sugars are high she gets very ornery and angry very quickly, when she is low she gets upset easily. For us we have her check her blood and adjust what we need to get her back on track.
I would suggest that when you feel a mood swing coming on, check your blood and self you are high or low ant track it for 15-30minutes. This will help you figure out if your diabetes is the cause of your mood swings. Then I would suggest that your contact your endocrinologist to the help you get in better control.
I hope this helps