Guessing it was hypercalcemia. Those are classic symptoms. 150,000 IUs a day is scary. I'm taking 5,000 which is probably more than I need.

For anybody taking D3 (or D2), be sure you're getting K2 (fermented foods, pork, Jarlsberg cheese). D gets calcium into your blood serum. K2 makes sure it gets to your bones. We can make K2 from K1 (green leafy vegetables) but most of us don't do the conversion well.

Also, I was hoping that link to 'lower risk of atherosclerosis' pointed at a study comparing supplementation to diet. It doesn't seem to. Personally, I'd expect that anyone supplementing calcium, particularly w/o K2, would be at risk of calcification of soft tissues. It's not clear to me that calcification of plaque is a 100% bad thing (well above my pay grade) but sealing those foam cells away from more phagocytes could be protective - so long as the vessel isn't occluded.