BYV says: It sounds like you may be pushing yourself too much in class. Try practising more gently for the next couple of weeks – not pushing yourself to your edge, which takes a lot of self-control. Keep a journal and document how you felt after each class and how hard you pushed. If you are increasing the number of classes and doing doubles, realize that is placing a lot of expectation of your body; as a result, you should move slower into and out of postures and in your day-to-day activities. Be aware of your form and alignment in class and out. Yoga will reveal your weaknesses. You have to become more aware and analyze your habits. Hope this helps!