heh, i got toasted a few times myself on this one. here's what u do (don't read any further if u don't want to spoil it):
1) med up to full b4 you go in as u will need most of you power
2) when u enter the circle, the threshing begins, so if you have any bodies in there, grab them quick! un-absorbed shards take away from your stats.
3) stand in the circle and take the beatings from the totems. yes, take the beatings. the meaning for this threshing is "are you a responsive healer?" so, you will get hit for damage, poison, etc and you need to heal/cure yourself enough so that you can stay alive through it. once you figure this part out, its not that hard... but gauge your damage with which heal to use, if u keep dropping arch heals when u don't need them, you will use up your power too quickly.
It seems like it lasts forever, but stick with it and you will succeed! have fun!!