But is it safe long term if you get more than 2 grams of calcium every day?In this video she says that her sickest patients needed to take up to 30.000 IU daily for a year after which tapering down to 10.000 IU. The most convincing research shows everyone needs 10.000 IU daily (from sun, food or supplement). Your 400 IU causing any kind of issue is a clear sign of absolutely severe deficiency and metabolic problems. You live in severe hibernation metabolism and any attempt at restarting normal function is too much stress for you to handle.
I recommend you try LE's multivitamin or similar proper product with broad spectrum of sufficient doses to try correct whatever is wrong. It has enough vitamin D to get you started, but after some time as things normalize you should target that 10k IU.