I haven't done it in a while (no time)- it can be fairly hard, but if you do yoga (or other exercise and balancing) regularly- it shouldn't be too bad. You will be soaked, like you jumped in a pool!
-One time I tried to make a different yoga class and changed my mind and went to Bikram... in terry cloth pants -i.e. a towel. I was holding them up and walking on the bottoms of these wet towels when I left! Needless to say, tight fitting or even a bathing suit- you move a lot and hold precarious poses- and you don't want to be falling out of your stretched out wet clothes... Just something to keep in mind
Also- it is 1 1/2 hours- so if your studio doesn't have a shower- you can't go anywhere after= so plan for the time accordingly.
Have Fun- it is a great workout- helping every major organ and joint in one session! Great to help along with the cleansing!