I'm not sure if you can become addicted... it's nothing I've heard about at least. You might check in with him; see if maybe your deficiency is just that severe. Perhaps you just aren't at a normal level yet, and the extra vitamin D acted more as a loading dose than a maintenance one?

I had an experience when I had severe vitamin D deficiency. I took a tablet and immediately felt a lot better. Like, amazingly better. However, I took the same doses later and did not have the same feeling, because the good feelings were related to me getting something my body desperately craved. After I hit appropriate levels there was no extra energy or euphoria - because this was based only on the deficiency.