I read your query.
You are hard working & brave boy , not having fear of Exam which many have.
During that day, U probably got an episode of " Hypoglycemia
( decrease in Blood sugar level ) with/without/or Hypo tension with less fluid level - less amount of water intake."
So u got an episode of Blackout
& sweating in excess with very short amnesia
U need to drink sufficient water means 8-10 glasses of water per day
& eat Food having glucose
in It like biscuits before Examination.
Ask any query again.
regards, DR JIGNESH