Just throwing this out there in case anyone else is struggling with this. My vit. D was suboptimal so one or more of my docs wanted me to take several thousand i.u.'s. After some time I noticed my energy levels were off. After about 6 months I finally realized it was an issue with sleep. I started going to a sleep doctor. I had two attempts at doing a sleep test, but for various reasons, was unable to sleep long enough to get any data to speak of. The doctor wanted me to work on sleep hygiene by reducing my daytime nap. I gave it try but failed after a few weeks, more tired and frustrated than ever. More months went by. I finally realized my feet were twitching again during sleep, causing me to wake up multiple times during the night. This was a problem I thought I had previously conquered by taking magnesium. So I increased my magnesium until I couldn't go any higher. It helped some, but not completely. It was ridiculous how much magnesium I had to take - about 2800 mg of elemental magnesium - like 5 teaspoons per day. Finally I was reading an ebook from Carolyn Dean regarding magnesium (she sells a super absorbing liquid mag that's not supposed to cause diarrhea). I got some of her mag and tried that in the hopes of finally being able to get in enough mag. But I had issues with the sorbic acid which is a preservative - only 4 drops caused achiness and an overall crappy feeling, so I discontinued. Then I remembered I had read in her ebook that if vit. D is supplemented over 1000-2000iu, it can cause a depletion of magnesium. I checked back in my symptom journal, and indeed, I had increased vit. D to 4000iu a little prior to the time I noticed my energy levels were off. So I tried reducing the vit. D. First I went down to 2000iu. My magnesium needs went down to 1400 mg. But I was still deficient. Finally I went down to 1000iu. Bingo! My need for mag has dropped to about 500mg. I am starting to sleep a lot better and feel more rested. It only took me 14 months of being a walking zombie to figure this out....:-( I hope this is helpful to someone!