Stress guarantees HIGH blood sugar, period.
Barring some other condition(s)/diseases, the all hormones caused by you body/mind enduring STRESS makes several things happen. If stress is a constant LOW level of stress, your body may well endure the adrenaline coursing through your bloodstream with little significant sign. Your body in effect gets used to it. The same manner your body can get used to ridiculously high blood sugar, not healthy that it does so but... it can anyway
IF stress causes your breathing to accelerate uncontrollably.... if your hands are shaking and cannot be calmed/slowed down, if your heart is tripping like a hammer in your chest..... if THESE signs are happening to you, your body is getting several stress hormones dumped into your bloodstream. Your adrenaline glands, your liver are dumping sugar into you so that you can run or fight with the thing which scared/upset you so badly.
The things historically which scared us as a species were meant for us to be afraid of. Today the emotional side, the physical aspect of that usually is not helpful in the same manner. My wife, the boss screaming violently gets-earns the fight/flight body chemistry but can be endured without any real threat to my body.
My body doesn't know the difference between the tiger which will eat me, and the same bodily sensations which a boss can generate without any valid threat to my staying alive in order to achieve them.