Well, there is a really good technique that I use for studying called the Pomodoro technique (Spainish for 'tomato') where for every 20 minutes that you study, you have a 5 minute break to relax, eat something or do something else extra curricular. Gradually, the more 20 minute sessions that you take, you get a longer break that is double the amount of time in your last break. E.g., first 20 min. session = 5 minutes, second session = 10, third = 20 until the fourth session is a full forty minutes. After this one, you repeat the cycle from the beginning. I find this technique really, really useful especially if I have an urge to create some art, or if I have a stressful day and need some down time. There are plenty of Pomodoro apps for iPhone and iPads, and you can also google the site's timer for a desktop counter.
If you feel the stress during the exams, talk to your supervisors for the exams and ask for Special Provisions. If you tend to feel cramps on your hand during the exam, ask if you can have a 5 minute break per half hour of each exam, and in order to apply for it you need a doctor's certificate or other substantial evidence that you are experiencing extreme stress during the exams (i.e. anxiety attacks). This form of provisions are perfectly acceptable during the HSC, and won't have any effect on your final marks and ATAR.
If you aren't stressed to that extent, go and talk to your school counselor or year supervisor and let them know of the stress you are going through. I hope that helps you a bit!
