I have had Hashimoto's for more than 30 years. Diagnosed by an endocrinologist in the early 90's. Levothyroxine overdose was the cause of much more violent internal "earthquakes" (is what i called them) for me. A functional Dr. (I found after 10 years of suffering and being told it was all in my head), switched me to Armour Thyroid (desiccated pig thyroid) - and I was a right as rain. He said that some people (like 10%) have trouble with the conversion of T4 to T3 (Levothyroxine is T4). Armour is a combination of T3 and T4. Most people can convert Levo (T4) to T3 as necessary. But he explained, that with an autoimmune disease like Hashimoto's AND with someone with conversion problems, the thyroid is still producing thyroid hormone - only the immune system is killing it before it can get to the cellular level where we "feel" better. Sometimes, he further explained, some of the natural thyroid hormone gets through and when combined with supplemental thyroid hormone, we can go into a state of "Thyroid Storm", or overdose. One theory was perhaps the immune system gets distracted from killing thyroid hormones, as in fighting an infection, etc., and the natural hormone is not destroyed, gets through the immune attach, mixes with the added / supplemental hormone, and bang - you have these "overdose" symptoms. Other causes can be in mixing T4 with for instance calcium supplements (the Tums are mostly calcium). There is definitely a calcium connection with the thyroid, / taking thyroid supplements. There is also a salt connection, particularly if you eat the common sodium chloride salt (AKA table salt). I had the most terrible thyroid storm once (with levo) after eating a huge hot dog, that was particularly salty. Same with taking calcium supplements at the same time as levo. That was way before they began to put the sticker on prescription levo / Armour, re: "do not take with calcium supplements". There has also been study after study that warns of using Flouride Bromide, or chloride (chlorine), (AKA Halides) as they can displace / attach themselves to the iodine receptors of the thyroid and again wreak havoc on the endocrine system, and any attempts we may be making towards supplementing an autoimmune disorder such as Hashimoto's. Health industry advocates would also point to stressed adrenals, however, mainstream medicine still does not recognize adrenals as contributory, for the most part. If one was to address adrenals, then things like coffee, alcohol, and other stimulants would be avoided. My experience in dealing with Hashimotos for all these many years is to eliminate as many inflammation-causing foods as possible (alcohol being number one - darn it!). Gluten / processed and fast foods being a close second. So many inflammation avenues that one must consider when dealing with any autoimmune disorder. And with Hashimotos, you must have a thyroid replacement hormone - you won't have any semblance of a normal life without it. The unbelievably sad part is - even if you find an endocrinologist who will run the thyroid antibodies test. (TSH, T3, T4 test alone won't find Hashimotos). they don't seem to want to do it! Recently had a family member who cannot pin down the many obviously hormone-related problems she is having, finally secured an appointment with an endo, and he actually said, "So what if we do find Hashimotos?" "There is no cure for it!" "Why do you want to know?" While there probably is no cure (There are those who say it is possible to put autoimmune into remission) - there is treatment! Thyroid Replacement Hormone!
The constant internal shakiness is most probably an imbalance of T3 / T4 in someway - regardless of whether it is undermedicated, overmedicated, or not medicated at all - or of an interference with replacement hormone, like calcium, fluoride, bromide (found in flour - "Bleached wheat flour" in the US - outlawed int the UK). That has been my painfully acquired education and experience. The good news? Once you start paying attention to when / how these episodes occur, (assuming you do have supplemental thyroid hormones of some sort) - life with Hashimotos can be fairly close to normal wonderful!