Anxiety is your brain's reaction to something around you. 
When you have a lot of stress, your brain starts sending out messages that can lead to you having a feeling of anxiety. Sometimes your fight or flight response can be triggered and that can lead to feelings of anxiety and panic
Facts about all types of anxiety
Anxiety and Social Anxiety Facts
Real teen's stories and facts about anxiety
Normal Anxiety vs. Anxiety Disorders
What to do when you are ready to take control of your anxiety