Yep, it's especially bad for people who don't get enough sunlight. If you decide to get yourself checked out for that, have them do a full panel of blood work on you and request they check for the vitamin D level. I forget what the target range is, and the consensus varies, but I've heard 80-100 is the average. My levels was <8 for Vitamin D2 and <3 for vitamin D3. That explained a lot, so I'm taking major supplements now.