Curious, do you get much sun? Vitamin D definciency commonly results in sickly people too.
http://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional...
Your body doesn't always exhibit signs of something wrong, and there are many instances in which that's it's true and it's too late to take action. I had to get a birthmark removed from my back last summer because it could've been a malignant type of skin cancer. I certainly didn't "feel" anything from it, and wouldn't have known about it until a dermatologist pointed it out to me.
These days it is common for people to avoid the sun and use excessive sunscreen if they do; geeks are not known for their tans. But a few minutes sunbathing is definitely beneficial.
The govt is a tad behind on this, but it has recently upped the recommendations.