A few hours after class, I get very stiff and painful in the back of the legs and this is worrying. So don't let the mind wander during practice. Don't be too aggressive or impatient, either. Think of alignment. Biomechanically you are very safe if you do postures in alignment.
Muscle imbalance creates a lot of problems.
Check to make sure there is good alignment with the left and right side of the quads. Balance with the foot in alignment and the weight in alignment. Remember, the body follows the eyes. Be careful to do the postures correctly, because you are creating an imprint that is hard to undo. Breath is the only way to affect the involuntary systems.