I have 4 deficiencies total.. D, so far is the worst! I cannot stand for more than 2 minutes, write more than 2 sentences.. I'm dizzy and exhausted and can't function.. HELP!! Dr put me on 4,000 of D a day. But I upped it myself after reading a lot. I'm on 8,000 a day along with Iron, Magnesium, B12 & C. Also occasional Biotin. I Feel horrible!