Well, the stress hormones cortisol and adrenaline raise blood sugar. If you are stressed mentally it stands to reason that these hormones could be raised which in turn could raise blood sugar. It is interesting to note that we have several blood sugar raising hormones and only one that lowers it - insulin (at least as far as I know).

My cat is diabetic, and when she's stressed her blood glucose absolutely SKYROCKETS. Generally this is brought on by going to the vet. Try to Zen out with some relaxation techniques and maybe some favorite music? You can also add in some physical activity to burn some of that excess blood sugar off.

I've also heard that because we're (sometimes) so low-carb our body's glucose levels are higher than you'd think. I think it was Chris Kresser who recommended eating higher carbs 3 days before a blood test to 'normalize' the glucose levels. I don't remember the specifics, but it made sense at the time.

Stress definitely affects blood glucose levels, my husband is type 2 diabetic and there are times even when he eats perfect that he has trouble keeping it in the low 100's.