Although my starting level was 20, I have a friend who had a starting level of 4. She raised her levels to normal range on 5000 IUs D3 daily -- she did indeed feel better, however, other co-existing medical problems, like high blood pressure, did not disappear when her D levels hit the normal range. You won't know the effect of vitamin D on your symptoms until you achieve and maintain a normal level. But, stick with it, and good luck!
I had more to say so I'm replying to my own thread.
I guess I've probably had these symptoms, severe ones, especially wrt mood and weakness. But I've just sort of learned to live with them. My doctors have all always told me, after batteries of various tests, that my problem must be psychiatric in nature as depression and mania and anxiety and panic do present with physiological symptoms.
I'd let myself become convinced I was merely lazy or that I was being a baby when I lacked the energy to perform basic tasks -- even, for example, bathing.
But I've been looking round the internet for anyone with as low a score as I (again, 4 units) and I've not been able to find one. Apparently I have been the living dead for some, maybe many years.
I regard this all to be very good news. After years and tens of thousands of dollars in out of pocket expenses for psychiatric treatment (my health insurance has crappy psych pros and they will drop me entirely if my actual diagnosis of bipolr goes into my record), I finally have some hope of relief.
I am probably still bipolar, or at least suffer from severe depression and/or mania. Definitely bad panic attacks and anxiety.
But the idea that there's a vitamin that could help with this? It almost makes me believe in God.