I had similar symptoms after about six flushes. I think it might have to do with the bowel getting clogged. When you say die-off symptoms are you referring to parisites? I say this because I did a half-hearted parasite cleanse aroung my fourth or fifth flush and thats when the symptoms started appearing (lethargy, greasy skin, exteme fatigue, and depression.) They seemed to get worse with each flush.
I did a Bowel Cleanse before my last (8th flush) and although I didn't really notice it at the time, I felt fine the next day. I am becoming a beleiver in doing these cleanses one at a time and with enough recovery time in between.