I agree wholeheartedly with @simondsa1 and @katgob
Sadly this is really common and no one warns us this will happen so it is very frightening. I remember the first night vividly (20 years ago) thinking oh my goodness, am I dying? Because I was suddenly just burning up and sweating profusely. It lasted an hour or so and then I felt wrung out and cold, so I put on a dry nightgown and went to sleep only to have it happen again and again.
After the third or fourth day it subsided, this coincidentally is about the time the fear about it subsided. They still came but milder, and decreased frequency.
I am still really glad your doctor ordered a PET/CT, if all it does is ease your mind, it is worth it. I also believe in making sure you have all the information you can have in order to make the best decisions for yourself.
How are you feeling now? Has your PET been scheduled yet?