During the fight-or-flight response, adrenaline and noradrenaline hormones accelerate blood flow to your muscles and brain, increase your heart rate, and relax your airway, so you’re better able to move around.
Cortisol is the most well-known of all adrenal hormones, and it helps your body use fats, proteins, and carbohydrates, increases blood sugar, and regulates blood pressure. Cortisol also plays a crucial role in your sleep/wake cycle and circadian rhythm.
Chronic stress causes high cortisol levels that trigger glycogenolysis and gluconeogenesis, which mess your blood sugar up even with a well-formulated ketogenic diet. 
During glycogenolysis, your body breaks down glycogen (stored glucose) in your muscles and liver into glucose (sugar) to give you immediate energy.
During gluconeogenesis, your kidneys and liver convert dietary protein or fat into glucose to use for fuel. Most cells in your body don’t need sugar to survive, but a small number do. Gluconeogenesis is the internal process and your body’s backup sugar source to prevent your blood sugar from dropping too low. It’s dangerous when blood sugar is way too high or way too low.
The HPA Axis
The signaling between your adrenal glands and your brain is called the hypothalamic pituitary adrenal (HPA) axis. During times of stress, the hypothalamus in your brain sends signals to your brain’s pituitary gland, and your pituitary gland communicates to your adrenals to release cortisol. Over time, your adrenal glands and thymus gland (an organ of your immune system) can gradually shrink with excessive stress and weaken your immune system.
The Role of Insulin
Your body decreases insulin secretion when you have a higher serum cortisol level. Insulin is the digestive hormone that helps scuttle blood sugar into your cells to keep your blood sugar in check at safe levels. If insulin isn’t being released properly, blood sugar levels become unbalanced. 
Chronic stress takes you on the road to chronically high levels of cortisol and lowered insulin secretion over time. High cortisol levels cause your body tissues to be less sensitive to insulin, so there’s more blood sugar available in your bloodstream. When this occurs, blood sugar levels can become dangerously high, particularly if left untreated.
Stress is especially dangerous for those with diabetes because a blood sugar spike could cause too much sugar in the blood to pass into the urine and trigger the body to filter out fluid, potentially resulting in a diabetic coma or dehydration.
Stress and Behavior
Stress can also lead to blood sugar spikes in other ways. People who feel stressed are more likely to participate in behaviors that could lead to high blood sugar. For example, people who feel stressed might engage in emotional overeating of processed and refined carbohydrates and foods that are loaded with added sugars.
People might give up on exercise and become more sedentary or forget to take medications if they’re supposed to. Stress can put a damper on your healthy habits.
Because your HPA axis plays a role in stress and sleep, if you’re under high stress, your HPA axis may be prompting the production of extra cortisol, leading to changes in the HPA axis. Research shows stress could impair restful sleep and change sleeping patterns. Not getting sufficient sleep can cause glucose intolerance, resulting in a dysfunctional metabolism and high blood sugar levels.  
Managing Your Stress