So, I am having a pleasant side-effect to the Vitamin D and that side-effect is, actually, pleasantness. A feeling of pleasantness. Like, if ordinary life is on a scale of puppies with “no puppies” being the worst day-to-day feeling you could have without feeling genuinely bad (warning, if you have a day to day feeling of any sort of number of dead puppies, you are probably depressed) and five puppies being the most awesome you could feel before being genuinely happy, I went from being a two-puppy gal to a four-puppy gal.
I don’t see “a general feeling of pleasantness” as a side effect of Vitamin D, but maybe because who would complain about it?
Tiny Cat Pants 
This is also why you’re in such a good mood after getting out of a tanning bed.
Not that I know this. :)
I’m so glad it’s working for you. Apparently there is a lot more to Vitamin D than we thought.