Worry is left-brain-focused and may keep you fixated on the details, preventing you from seeing the big picture of a situation which may be more scary. Some researchers suggest that worrying may be a way of avoiding the bodily signs of anxiety and stress such as your heart beating rapidly or negative mental images related to your stressor. Worry can also give you the illusion of control over future outcomes. Some people believe that if they stop worrying and relax, they'll be caught unawares by some devastating event, so they keep planning and preparing to prevent or avoid failure.
Clinically, excessive worry is the primary symptom of generalized anxiety disorder (GAD). Evidence seems to indicate that the content of worry in people with GAD concerns similar topics to ‘everyday’ worry, but that it is often concerned with more unlikely or remote events. The terms ‘hypothetical worry’ and ‘real event worry’ are often used to describe this distinction. Other important differences are that people with GAD often experience their worries as uncontrollable, and will worry habitually instead of in response to particular triggers.