Oh @ Greydog > Just seen your post. I know it's really scary, and I how much you worry. Although our current rescue doesn't seem to be bothered about thunderstorms, he is terrified of absolutely everything else.
However, our three previous rescues have always been scared out of their wits during thunderstorms. I also had the fear that the panic would cause a heart attack. It never did. We have what was probably previously a larder where our washer/dryer is. With the boy we had before the current one, if I knew a storm was due, I'd save up the washing. I'd then put his rug in that space and put the washing; then the dryer on. He'd go in there and it certainly helped to some extent. Small space, warmth, and noise of machine.