My Nephew Is 14 And He Fainted Today At School.

My nephew is 14 and he fainted today at school. It was only for a few seconds and he experienced minor twitching according to his friends who called his name as he remembered when he came out of it. He is a borderline diabetic and all appears to be normal at this point, he will be visiting his dr today for further testing. He seems to be on the computer for a long time and does not sleep enough. He also frets looking at blood and for that reason reluctant to take a blood test as he faints everytime he does.
Could you please advise on what may be the possible cause and what tests to ask for.
Thanks.