We think that certain changes in brain chemistry and activity are associated with each anxiety disorder, although our knowledge about this is far from complete. Panic disorder seems associated with a lowered threshold for, or spontaneous firing of, certain alarm systems in the brain, like having a burglar alarm that goes off when the wind blows strongly, or even discharges randomly, instead of only when someone is breaking into the house. There are several hallmarks of an anxiety disorder. One is extreme anxiety, fear or nervousness. This can be episodic, such as having panic attacks once a week, or chronic, such as having GAD symptoms on a daily basis.
Trouble falling asleep or staying asleep is a common symptom of generalized anxiety disorder.
Another marker of an anxiety disorder is a desire to avoid situations where you used to be comfortable, or where you need to go to function successfully. Certain other conditions may produce symptoms that look like an anxiety state. Depression may be associated with nervousness, sleeplessness and social avoidance. Medical conditions like hyperthyroidism can produce nervousness, trembling, sweating and rapid heart beat. Excessive use of caffeine or other stimulants, or withdrawal from tranquilizers or alcohol, can produce symptoms that mimic an anxiety disorder.