Anxiety may be a symptom of other mental health problems, eg depression or alcohol dependence. It can also be caused by substances, eg LSD, ecstasy or caffeine, or by withdrawal from medicines taken long-term, eg tranquillisers. Sometimes anxiety can be associated with a physical illness, eg thyroid disorder. For this reason you should see your GP in order to rule out a physical cause. Your anxiety could be caused by some sort of stressful life event or if you witness something traumatic. In many cases this sort will lessen after a few weeks. It would only be considered an anxiety disorder if the feelings were severe or long-lasting and were interfering with your every day life.
Attribution: BUPA