Hmmmm that is strange! I could/would agree with your son except it didn't happen with your 1st knee. The only time the heavy chills hit me was right after I got home from the hospital. I'm never usually cold, especially in July so it took me by surprise but I chalked it up to the surgery, trauma, meds, pain, and all that goes with this. It has never happened again. I think if you are anemic it can make you chilled and very tired. Maybe you should have that checked? Or, possibly the exercise is somehow affecting your blood pressure? Now, the moving aches and pains I TOTALLY get. It just seems to move around day by day practically. Good days, bad days and in between days and it's very, very, very frustrating. Ask your PT about it next time you see her and see what she says. I hope it stops happening cause that is really weird and kind of frightening for you I'm sure.