One of the great joys of playing a musical instrument is the feeling of being able to share the music with other people in the form of a performance. Yet something which is capable of giving both performer and audience such a feeling of mutual wellbeing, can also lead to a negative experience - often known as "stage fright".
The anxiety leading up to an exam or concert can result in many different experiences. While some people feel excited or exhilarated, others may experience less pleasant feelings - ranging from a loss of sleep or appetite, unsettled tummy, cold sweats, shaking and loss of confidence.
It is important therefore to cultivate the idea of "giving" the music as if it were a gift to the listener. After all, as a recipient of the gift, the listener will respond graciously, as if it were a present. Every time you play, try and "give" the music to whoever is within earshot - whether it be the postman at the door or your neighbour putting their clothes out to dry!
Secondly, try to start each playing session (I personally don't use the word "practice") by singing with real gusto. Then try singing through some of the music you are going to play, even if it's a scale. Finally, try singing whilst actually playing the piece. The physical act of singing is the purest form or music making and has an astonishingly liberating effect, both physically and emotionally. Done regularly, you can cultivate the continual internal "singing" all the time as you play, so it never becomes a purely intellectual exercise.
If you and your teacher have decided that grade exams are for you (and not all pupils will want to do exams) , just remember that the examiner is a human being who has to sit through up to 5 exams an hour for a large portion of their day. No doubt, they have witnessed their fair share of nervous candidates and therefore if you're able to give them a little joy in your music making, it will lift their spirits and may even make their day. After all, they may be tired by they time of your exam and in need of a litte "gift" !