Vitamin D deficiency? Mine was about half of "normal" and I'm on a HUGE weekly dose now. I have to go for more bloodwork to see if that will also solve a few other problems. I get so, so sleepy sometimes. One day in the summer I walked from the kitchen to the office, maybe 20 yards? I could feel myself sinking so I tried to walk back to my car, to drive home (less than 1/4 mile). Instead I opened the hatch, closed it back, and slept on the floor for over an hour.
It happened several times like that, and really scared me because in the off season I'm the only one home with my 2-yo. Luckily I haven't had anything nearly as bad since taking the vitamin d. What's REALLY funny is that I was looking up good food sources of vitamin D and found that one was fish, and one is egg yolks. So two summers ago I got on this kick and I was eating eggs with spinach/pumpkin seeds/sunflower seeds, etc. every morning, and either tuna on salad, or herring/sardines every day. I never felt better in my life. It's so funny when our bodies know what we need.