I went to the doctor about eight months ago for an unrelated ailment, but the doctor wanted to do some blood tests. Turns out I had a fairly large vitamin d deficiency.

The doctor told me just to pick up some supplements. After a couple weeks I was genuinely surprised how much better I felt. Overall less lethargic. I've been feeling over all just kind of blegh for a long time and it really seems to have helped.

My dad had suggested vitamin d and I didn't take it seriously but he was right.