Having worries at times is normal but people suffering from Anxiety Disorder develop excessive un-controllable worries. They have faulty beliefs (Metacognitive beliefs) which give rise to persistent anxiety.
There are 2 types of worries:
(1) Type-1 Worry: Any negative thought leads to a thinking process about a range of potential threats and ways to deal with threats. Patient believes that worrying is important to be prepared for and coping with stress.
(2) Type-2 Worry (Meta worry): This is fear of worry. The patients with Anxiety Disorder develop fear of worry, they feel they wont be able to control their worries and worrying will have harmful effects on their health like heart attack.These beliefs lead to the development of certain faulty behaviours in people with Anxiety like reassurance seeking and avoidance which further aggravate the anxiety.