There is a lot of evidence that Iodine will liberate heavy metals from the body. This inherently requires the metals to somehow first be liberated, and then excreted.
It could be that your Iodine dose liberated heavy metals, that did not get excreted but rather, re-settled somewhere else, or were only partially liberated and moved a little.
I used to have palpitations also, I finally came to the conclusion that it had something to do with an electrolyte issue, after reading a Japanese study on heart attacks and preventive supplementation that included taking magnesium, and the amino acid taurine. For this, magnesium taurate is also sold, to get both in one medicament. I used taurine and magnesium and when I did my heartbeat always returned to normal within about 15 minutes, if I put the taurine powder and/or magnesium in water.
I can't tell you what to do, but if it were me I'd look at what electrolytes I'm getting, and which I'm not.
I would load my body up on sulfur, maybe MSM, R-lipoic acid, with the theory being that the sulfur would bind any metals like mercury, cadmium, etc. Those are divalent, and after the sulfur I'd add cal, mag, and zinc.
I'd also take a lot of potassium in the form of the chloride, and I have done this, like 10-15 grams per day of potassium. My favorite way is to make a 1% solution in water and drink it, because that's basically the concentration of the saline solution they use in medical practice for IV's. At first I was afraid of potassium, until I looked at the LD50 for KCl and realized that in order to kill myself I'd have to eat way more than 100 grams of it.
I don't know your answers, only a gut feel, that you have some metal ions in the place of where other electrolytes are supposed to be, either that or a deficiency of an electrolyte.
Selenium is also essential for metal detox, if that's your issue. Selenium is necessary for the body to make glutathione peroxidase, an enzyme the body uses to remove metals.
Lots of ascorbate also, is never bad.
I hope any decision you make or course of action is not based on me telling you what to do, because I am not. I am only sharing my personal observations, and inviting you to learn more if that is what you want to do.
Good luck, I wish you the best. I don't think God gives us a problem without also giving us the ability to find a solution