Hi amtxo, I have experienced the internal tremors as well. It is in the back of my head, spine and hips. I have hashimotoe's (autoimmune thyroid disease) but not hypothyroid as of yet that I know of. I also experience neuropathy and weird imbalance issues like I am walking on sand or bouncing up and down really fast even though I am walking on normal ground and not bouncing! It's worse after using elevators and wearing heeled shoes. I have no diagnosis yet but I wanted to let you know that internal tremors I looked up may be harmless. I to do not know what causes it but I will keep you updated as I am undergoing test and treatments.