Ever since my fusion surgery with instrumentation on feb 22nd, I have had hot/cold flashes that I hadn't gotten before. My dr has heard of patients explaining to him the same thing. They think its due to the hardware. That's my "cold" story.
I have screws and rods in my back from a PLIF at L4-5 and a plate like you at C6-7 and the cold has the same effect on me. Its pretty common.
I have metal in differant places i feel the cold in all those places it is not uncommon