Well. Even back then, the legend wasn't fragile, at least not mentally or psychologically.
The soaring and plumbing started with his winning the Heisman on December 1, 1990, after a record-setting season for the Cougars. As C. Peter Lambos of New York's Downtown Athletic Club declared him "this year's greatest football player," the junior quarterback's teammates celebrated by chucking him in the swimming pool at the Princess Kaiulani Hotel, where BYU was staying before it played Hawaii to close out the regular season.
That celebrating lasted all of four hours. Thereafter, the Cougars got crushed by the Rainbow Warriors by the count of 59-28, a result that Detmer subsequently described thusly: "It was a disaster, we got our butts kicked.