Hot (or Bikram's) yoga is a ninety minute moving meditation that consists of 26 yoga postures (done twice each) and two breathing exercises, and it is practiced in a room kept at about 40 degrees Celsius (105 fahrenheit). it's fairly strenuous and you sweat A LOT! i have never sweat so much in my whole life, actually. you have to keep a towel on your yoga mat or else you will literally make a puddle of sweat around you. some people can feel a bit faint or nauseous. it is incredible for mental/emotional and also physical detoxification. not to mention, it makes you stronger, and increases your balance and flexibility. it also REALLY sculpts your body.
it may be soon to tell, but i really think that practicing hot yoga on my fast is reducing my detox symptoms. i don't think this kind of "active fasting" is for everyone though... if your body is feeling totally exhausted and weak you should just rest and do as little strenuous activity as possible :)