Truth be told, it was a pretty awesome workout and a good testimony to the 50% harder work than cycling alone theorem. Kind of like people who go to Weight Watchers meetings lose multiple times more weight than people who diet alone (oops, pardon my shameless, self-serving plug!).
So what's the moral of the story? Talk smack to your spinning instructor. You just might get an even better workout. Or you might hurl. Either way, nothing risked, nothing gained.