tflory…..My husband also had these episodes of chills (also called rigors.) They are not uncommon and have been reported often on this site. In fact, the Search function will lead you to numerous, previous discussions. They come on unexpectedly and seem to take their course within a few minutes to somewhere around 1/2 of an hour. I would grab the feather comforter and wrap myself around my husband until it stopped. (He said that this was one of the better moments with this disease.)
A nurse mentioned that it had something to do with the nerve endings being affected by something although; she did not know what that something might be.
I wish I had a better answer for you, but sometimes it helps knowing that others have had similar experiences.
All my best wishes,
Marion