I joined up to my first yoga class once.... holy moly! I should have done my research, I had joined up to hot yoga and it was torture. There was I expecting a very relaxing evening of stretches, followed by 10 minutes lying flat on your back (cool down)... err... no! It is not recommended for newbies, although I have to say it makes you realise how fit and supple you need to be to undertake that type of yoga.
Yoga always looks so serene, but I have to say on the occasions I have done yoga I look anything less than serene, I find the warrior quite a difficult pose to maintain with poise and dignity. So I can appreciate the calories burnt trying to maintain the simplistic look.