When doing mock exams i find it very difficult to stay focused after 30-40 minutes and i have to take a break, i cannot imagine taking an exam that is 2,5 h long Do anybody know of any legal substances that could help me stay focused and improve the speed of solving tasks ? Caffeine is not an option - it makes me anxious.
Take a 30-60 second break. Seriously. I stretch/flex my feet (without getting up) and look away from the computer periodically during an exam. It keeps my energy up and helps me sit still that long.
Stop fretting over it, the bigger you make it in your head the more it'll affect you. Try keeping a casual focus instead of the situation where you almost plant your eyes on the screen (I used to do it, a friend of mine pointed it out to me). Lastly, you'll just get used to it and your attention span will increase in some time.