Anxiety affects us all. It is a feeling of unease, worry or fear.
It is normal in different situations, e.g. sitting an exam. In some situations anxiety can be helpful, e.g when crossing a busy road as it can make you more alert and aware. We all worry and it is useful when it leads to problem solving.
Anxiety becomes a problem when it is so severe that it stops you from doing things you need to do, when there is no clear reason for it, or when it lasts for a long time.