I had a bunch of labs drawn and was also tested for Lyme Disease as well as other things. I was diagnosed with Vitamin D deficiency about a month or so ago.
Even though I work night shift, I felt very lethargic all of the time. It wasn't exhaustion from working nights, just not having energy to ever do anything. I was also started on a Vitamin D supplement and have felt a little change.
Although Vitamin D deficiency is very common, I was surprised to find out that I was deficient because I live at the beach so I get plenty of sun, I don't suffer from milk allergies and I don't adhere to a strict vegan diet which makes people more at risk to become deficient.