http://www.labtestsonline.org/understanding/conditions/vitaminb12.html Vitamin B12 and Folate Deficiency
B12 and folate are B complex vitamins that are necessary for normal red blood cell formation, tissue and cellular repair, and DNA synthesis. A B12 and/or folate deficiency reflects a chronic shortage of one or both of these vitamins.
Since the body stores 3 to 5 years worth of B12 and several months’ supply of folate in the liver, deficiencies and their associated symptoms can take months to years to manifest in adults. (snip and I added emphasis)
Over time, a deficiency in either B12 or folate can lead to macrocytic anemia, a condition characterized by the production of fewer, but larger red blood cells and a decreased ability to carry oxygen. Patients who have this condition may
tire easily, be weak, and be short of breath. A deficiency in B12 can also result in varying degrees of
neuropathy, nerve damage that can cause tingling and numbness in the patient’s hands and feet and mental changes such as confusion, irritability, and depression. (emphasis added. Also, while I didn't get any anemia tests done, the symptoms are way too obvious to be a coincidence. Not for my age.)
(snip).
Oh, "irritability" is too right. While that ties into an admitted anxiety condition, the fact that B12 supplements have only helped me feel more at ease is proof that there's a lot more going on that nobody within the clinic even bothered to look for. (a 3rd party neurologist, who was outside the clinic had done the test. I sure as hell would not trust anybody within the clinic. Not by that point. And I was right.)