In The Wednesday Wars by Gary Schmidt, why did Holling become overheated on the day of the state achievement exams?

Before Christmas break in The Wednesday
Wars by Gary Schmidt, Mr. Guareschi, the principal of Camillo Junior High
school, announced that all junior and senior high students would be taking the New York
State Standardized Achievement Tests in January, after the break. He sent home practice
tests for everyone to work on, as well, hoping that students would study over the
holidays. Holling Hoodhood's teacher, Mrs. Baker, thinks such testing is ridiculous and
refused to give her students the practice tests.

The day
before the tests are scheduled to be given, Long Island is hit with a serious snowstorm
which knocks out the electricity in the school. This means no heat and no lights, not to
mention dangerous driving conditions for the buses; however, Mr. Guareschi makes it
clear that the tests will still be administered and every students is expected to be in
attendance. 

The testing day begins without electricity,
and Holling is prepared. 

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Since the power was still off at the school, I
wore thermal underwear--top and bottom--plus an extra T-shirt, a sweatshirt, and two
pairs of heavy socks.

He was
sweating on his way to school, but he believed he would be "warm and cozy through the
test, even if he couldn't move [his] toes in [his]
boots." 

Unfortunately ]for Holling, at least], the
electricity--and heat--returns in the afternoon, and suddenly Holling finds himself
nearly fainting because he is so overheated.