Going outside in the sun is great! (if you can find it and get there)
Vitamin D deficiency is actually pretty common (especially here in the Pacific Northwest), and can make you feel crappy and tired.
http://www.webmd.com/diet/guide/vitamin-d-deficiency#1
http://www.healthline.com/health/vitamin-d-deficiency#overview1
Ideally, you could take advantage of the sun when it’s out, participating in fun, outdoor activities like hiking and picnics and frolicking and having adventures with your friends and loved ones!
However, when you can’t leave the house and don’t want to interact with people, but you know that vitamin D is good for you, just go somewhere as private as possible that is in the sun. If you don’t feel able to make your way to some special nook in your favorite local park, take advantage of your yard (preferably the back yard). A friend or neighbor’s yard will work too! I usually sneak out around back and hide in the corner of the yard where no neighbors can see me. Sometimes I bring a pillow and soothing cool beverage, and if I’m ambitious, a book.
Just don’t forget the sunblock.