I hesitate to mention this at all, because the symptoms you mention sound dangerous, and I don't want you to say, "Oh, that's all it is" and put it out of your mind. It's just one possibility you could discuss with your endocrinologist. Here goes.

Hashimoto's, as you know, is an autoimmune thyroid disorder in which your immune system attacks your thyroid gland. As the gland dies, it's unable to produce enough thyroid hormone, so you're hypothyroid. However, sometimes as some of your thyroid cells die, they can suddenly release stored-up thyroid hormone. So some people, in the earlier stages of Hashimoto's, have surges of thyroid hormone so that they actually have hyPER flares, against a background of hyPO-thyroidism. A surge of thyroid hormone would make your heart race. I'm not sure about the pain, pressure and tightness, and I don't think it would explain the back aches.

This stage of Hashimoto's is known as "hashitoxicosis." It usually goes away on its own as the disease progresses. It might not show up on the lab work.

Again, this is just a possibility, but worth discussing with your endocrinologist. If you don't have an endo, get one!

I hope some people with Prednisone experience will chime in on this. It can make your heart race too, I think.

Abby