My experience is with Iodine at a much lower dosage (up to 12.5 mg) and I eased into it over months. Even still I got pretty bad kidney aches and sinus drainage, both have since resolved more or less. And my diet is very clean, wholesome. So it is very probable that a much higher dose taken too quickly can knock someone flat.
Also bear in mind that Iodine is an anti-microbial (yeast, bacteria, virus) powerhouse. If you have some sort of systemic infection, even if you are asymptomatic and don't know of it, a fast die off can lead to an intense reaction. Perhaps most common are flu-like symptoms experienced during a Candida die off. However such symptoms usually go away within a couple of weeks.
And so in my opinion, unless you have compelling reasons to the contrary I would be very respectful of iodine's potency and proceed slowly. Oh, and of course be very mindful of the companion supplements.