One of my sisters has a hot yoga studio. I've sat in on a few of her hour and a half sessions and while I can get through it, I'm always praying for the end. The sweat POURS off, I want to die, but I feel refreshed after I cool down. I rowed for 2 years on a varsity college team and bikram is up there with some of the burly workouts we had to do. Maybe your body is acclimating to the intensity of it.