Stress has a significant effect on my BG.
My morning fasting readings are much higher on a day when I will be busy, or stressed. Job interviews and such send it silly-high.
A cold, virus, infection or tummy upset will affect BG too. As will severe or long term pain.
Prolongued stress also seems to eat up BG out of my blood, sometimes causing me to hypo. This could be anything from new job, to travel, or a big work project.
Busy mental work also 'eats' up BG. If I attend a training course, or take an exam.
The answer (to ALL of these stresses) for me, is to keep strictly to my LCHF way of eating, monitor BG regularly, be alert for the signs of a hypo, and keep suitable snacks to hand. I am Type 2, diet and exercise.