Although this phenomenon does occasionally interrupt upper-year classes (McGonagall and Flitwick keep a running tally of accidental magic incidents in their NEWT classes, and anyone with more than one in a week gets remanded to Madam Pomfrey to be force-fed a sleeping draught), it does not usually cause any trouble at Quidditch games. Fifth- and seventh-year students typically make up less than a quarter of the players and of that number not all are as concerned about their examinations as their peers; and in any case just one night of missed sleep is usually not enough to exhaust a teenager sufficiently to cause problems.