What are the aspects of stress causing blood sugar spikes and declines?

Hormones: Stress produces stress hormone (cortisol) and adrenalines which counteract the effect of Insulin making it less effective. When Insulin doesn't work well, your blood sugar goes up. Some people overcompensate (overtreat) for the high blood sugar and has a drop after the initial stress hormones are cleared from the body.

Insulin resistance: Stress hormones (cortisol) can make your Insulin less efficient, and if high over the long run, can contribute to obesity, which also makes Insulin less effective. When Insulin doesn't work as well, sugars can rise.