I can't imagine painting alone would bring on enough Iodine to cause a detox headache.
Are you doing salt loading? Selenium? Extra C? Extra water? Calcium/Magnesium? These all help reduce or eliminate any detox headaches or other detox symptoms of Iodine consumption. But if you're only painting, I think the headache was something else. I could be wrong. Many more here smarter than I am about this.