I don't recall if you mentioned being on any medications, but I want to throw this into the mix. If you're taking anything which raises serotonin levels, either prescription medications or supplements such as l-tryptophan, 5-HTP, arginine, maybe phosphatidylserine, or even eating high starch a lot, you should know that 80% of the body's total serotonin is located in the enterochromaffin cells of the gut, where it is used to regulate intestinal movements. Since serotonin influences peristaltic action of the colon, too much or too little can result in constipation.
If we didn't have any good experiences, we wouldn't continue using iodine. We're no different from you. Before I found this forum, I had an overwhelming need for iodine due to fibrocystic breasts and a fear of breast cancer. But when I took it, I became convinced I was poisoning myself and that the headaches indicated I already had enough iodine. I stopped. It made me afraid to think that my body had symptoms of needing iodine, but I couldn't tolerate it. The strength of this forum let me know that I was not alone, and that working through the detox I would eventually see the other side. I was older, and felt that time was of the essence, so I pushed past my comfort zone. You are younger. There is time for you to take it very slowly if that's what you want. Take one or even one-half Iodoral, or one or two drops of Lugol's 5%, or 3-5 drops Lugol's 2%. Let your body take it in quietly and don't push. Just make it part of your every day, and don't think about it more than that.
Oh, it be, alright. You want just the right amount of serotonin, not too much, not too little. I have fought this dilemma myself. It's the curse of having a needy serotonin-seeking brain. Some days it seems as though I get to either sleep (enough serotonin) but have a big belly with slow movements, or toss and turn all night (not enough serotonin) and have a flat stomach with easy movements. I'm working on fine-tuning this for myself.