The perk-up began with the opening ceremony but took hold on Aug. 1, when the cyclist Bradley Wiggins, the first Briton to win the Tour de France, became the only rider to have won the Tour and an Olympic gold medal in the same year.

“Whatever happens from here,” a columnist for The Daily Mail wrote, “it will be hard to top this.”

But the golds continued: seven more in cycling, four in rowing, three in equestrian. There have been British golds won in the cathedrals of English sport, like Andy Murray’s tennis victory at Wimbledon, and in events that most people would be hard-pressed to define, like men’s keirin. The Duke and Duchess of Cambridge have been seen at events displaying get-a-room levels of affection, and articles have appeared in the news media exploring why the British had not won gold medals in a given event rather than the more characteristic converse.

But what had been a balmy Olympic fever became a roiling epidemic on Aug. 4, when the British had their greatest night of track success ever, with a gold in the long jump, Britain’s first gold in the 10,000 meters and Ennis’s golden smile coming across the finish line in the final event of the heptathlon. With that, the whole of Britain seemed nearly to come unglued.

“I’ve been in the Millennium Stadium when Wales have clinched a last-gasp win against England in the Six Nations,” wrote a sports reporter for The Western Mail, a Welsh paper, describing a rugby triumph, “but I have never heard such a noise as that which erupted on Saturday.”

This is saying something indeed. While England’s St. George’s cross, Wales’s red dragon and the Scottish saltire are all common sights in soccer season, as the kingdom un-unites in rooting partisanship, a Union Jack is typically a rare find.

That is no longer true. “I’ve never seen so many Union Jacks,” Rachel Dickens, a teacher in Sheffield, said. “They’re on cars and houses in people’s gardens.”