For anyone that reads this post…here’s the advice from a regular practitioner of 3yrs. As far as I can tell, there is no harm in doing a “double” from time to time. However, I’d recommend spacing the classes out by a few hours. So, for example, if you do a 12:00 noon class, the next one could be 6:00 PM or later. Overall, I would not recommend making a habit of 4 classes in 2 days. Your body needs time to recuperate from one class, let alone two in one day. Bikram yoga is not any different than other forms of activity. Some moderation is necessary because your body needs time to take in the benefits. Consistency is the key to a good practice. So, the bottom line here is that a “double” is a fine way to challenge yourself. But making it a habit to do four classes in two days is not going to bring the benefit you imagine.