Yoga class is usually not aerobic (this semester -- last term I was in a "vinyasa" or "flow" class that had me puffing and
Parsvotanasan ("Pyramid Pose"). [Like this picture, except I only got my back as low as parallel to the floor.] Despite the non-classical result, I actually got a compliment from my Yoga teacher, who said my pose was "powerful and relaxed". Well, maybe... I did get a better thigh-bone position than ever before in the pose.
The session always ends with a cool-down, usually legs-up-the-wall (lying on our backs) followed by Savasana ("Corpse Pose") for deep relaxation. To me, Savasana is like dessert after the meal!