Stress results when something causes your body to behave as if it were under attack. Sources of stress can be physical, like injury or illness. Or they can be mental, like problems in your marriage, job, health, or finances.
When stress occurs, the body prepares to take action. This preparation is called the fight-or-flight response. In the fight-or-flight response, levels of many hormones shoot up. Their net effect is to make a lot of stored energy - glucose and fat - available to cells. These cells are then primed to help the body get away from danger.
In people who have diabetes, the fight-or-flight response does not work well. Insulin is not always able to let the extra energy into the cells, so glucose piles up in the blood.
Many sources of stress are not short-term threats. For example, it can take many months to recover from surgery. Stress hormones that are designed to deal with short-term danger stay turned on for a long time. As a result, long-term stress can cause long-term high blood glucose levels.
Many long-term sources of stress are mental. Your mind sometimes reacts to a nondangerous event as if it were a real threat. Like physical stress, mental stress can be short term - from taking a test to getting stuck in a traffic jam. It can also be long term - from working for a demanding boss to taking care of an aging parent. In mental stress, the body pumps out hormones to no avail. Neither fighting nor fleeing is any help when the "enemy" is your own mind.