Could anxiety be caused by other reasons besides depression/stress/worry?

Anxiety: Anxiety is a description of an emotion, a collection of symptoms, and even a category of mental illnesses. Depression, stress, and worry are equally big labels with variable meanings to different people. Symptoms of anxiety can result from many sources, including physical conditions such as hyperthyroidism, certain occult GI tumors called pheochromocytomas, alcohol ; other drug withdrawal, etc.