I don't know if you're still looking for an answer.. but the reason you bg's may spike is because of the stress that's put on your system in Bikram Yoga -- when your heart rate goes up and your adrenaline is pumping from intense activity you can be a little insulin resistant at first.
Don't bolus for the high BG you see immediately following a class. Bolus for half. Or better even, eat something with carbs, and bolus for the carbs you eat. Then check your bg again 2 hours later and I bet you'll be back on track.
I'm a bike racer and bikram yoga doer -- and I can tell you again and again.. extreme exercise that puts stress on my system, no matter the length artificially spikes my bgs.
Hope this helps.
Amen to that.
I do bikram and am type 1. I go higher after class from the exertion and intensity of the exercise. I think it is cortisol related. I bolus after class rather than before to avoid being low. I don't eat before because I go in the morning and get nauseous if I do. I find that a vinyasa calss brings me downa nd I stay down, but with bikram I go up. My class get to 105 degrees- pretty hot! maybe that's why.