Try some relaxation exercises. These will show you how to loosen the muscles in each part of your body. They will also train you to make your breathing slower and deeper. You can hardly stretch out in the middle of the classroom, put on some tranquil music and start doing relaxation exercises. However, you can take a two minute break in the stock room and do some breathing exercises before a particularly difficult class.
Anxiety is caused by fear.
This fear is fuelled by negative thinking. It often feels as if there is a chatterbox inside your head filling your mind with a constant babble of doom and gloom. When faced with a demanding class or a challenging meeting, this chatterbox floods your mind with dreadful thoughts. However, you can use the power of your mind to replace these negative thoughts with more positive ones. One method is creative visualisation.