D, what you're referring to is "peroxide-induced necrosis". The GOOD news is that selenium deficiency is RARE, however, IMO, you can't rely on Brazil nuts to supplement selenium. The selenium content varies too much.
One thing that I have seen recommended is to support your body nutritionally BEFORE beginning Iodine supplementation. Sunflowers, I would recommend backing off, & making sure that you're getting all of your companion nutrients FIRST.
And then, start over & up your dose gradually. BTW, the tiredness may be a manifestation of bromide detox(a GOOD thing). Not a good thing, though, if it's incapacitating. Build a strong nutritional foundation FIRST and THEN begin supplementation. Detox is easier when it's gradual, IMO.