My doctors have not been able to explain this, and noone at the YMCA where I swim has heard of it before. I have been swimming regularly for forty years with no problem until seven months ago, when on many of the evenings, nine to twelve hours after I have swum a half mile in the early morning, I get a low fever, flushed face, and chills. I never get these symptoms on days I have *not* been swimming. Taking two Extra Strength Tylenol has taken care of it each time, and I am fine in the morning. But I have given up swimming for now, because this is unpleasant and may be something my body is trying to tell me.