Feel great one minute and then hit a wall of fatigue

Hi All,
I'm female, 37, and been living in Phoenix for 4 years. Diagnosed vitD deficient this September (also borderline anemic; all other levels normal) at the student health center.  Level was 14 with minimum level 30. Symptoms were fatigue for no reason, extreme difficulty concentrating, and feeling dizzy. Prescribed 50,000 units D2 per week for 14 weeks; I'm about halfway thru.

Dizzyness is gone and fatigue / confusion improved right away upon taking prescription. Another bonus is that I used to wake up feeling depressed (last 10 years or more) and now I wake up feeling fine.
But, last few weeks I started to feel worse and worse so I started to read online info. Started taking magnesium supplements last week (400 mg/day of amino acid chelated Mg) and that helped a lot. Taking a multi for other vitD cofactors (vit A, vitK and boron).

My question is, some days I have a great day, plenty of energy and mental clarity and then hit a wall of fatigue, like flipping a switch. Does this happen to you guys? I understand that it can take up to a year to regain health *after* vit D levels are restored, but this sudden switch seems weird. I'm a PhD student in molecular biology, and while I don't specialize in human health, the sudden onset of fatigue doesn't jibe with what I know about basic physiology.  

Also wanted to recommend this great site: http://lpi.oregonstate.edu/infocenter/vitamins/vitaminD/
Linus Pauling won two Nobel prizes and was a pioneer of the benefits of vitamins in human health; his good work continues at the Linus Pauling Institute at Oregon State. The site gives recs on vitamin supplementation based on the latest reputable studies, so it's more informed and up to date than US RDA  or local docs.
Anyway, thanks for your posts and hopefully we all feel better soon.  

[beckyscience]

I forgot to mention that I also started supplementing 400 IU of D3 per day. Will up this to 800 IU of D3 per day.

[arbguy]

Yes, I have had that feeling a few(3-4) times. On some days, when I am doing relatively OK, but out of nowhere I feel a "surge" of fatigue and my fatigue/confusion deteriorates quite a bit. I hope we get better.

[beckyscience]

Thanks for the reply. I also noticed that I could "flip the switch" the other way; if I'm feeling very tired I take 400 IU D3 and about 20 minutes later suddenly get all my energy back. Weird.