When I lay down to sleep, winter, spring, summer, or fall, I often get a tingling/freezing sensation starting at feet and going up through body -- cold to the bone -- yet burning as it progresses. lasts only seconds and comes and goes. Normally when I lay down to sleep, but occasionally other times. Almost EVERY time I lay down to sleep. I already have hypothyroidism and my levels are adequately controlled with Levothyroxin. What might this be? Thank you.