Consider the possibility that the high B12 (also how's your B9-folate level?) without taking supplements means either you have kidney failure, or, if the kidneys are fine, your kidneys are hanging on to it for another reason such as your body NEEDS it. Why does your body need a high level? We have human genetic variations such as the MTHFR genetic variation which reduces capacity to methylate it and therefore use it. See here: Folate Although it is related to some mental illnesses, that article also talks about other neurological manifestations, and explains about MTHFR. And here for Nutrition and Epigenetics

You may want to have your homocysteine level checked. That is a measure of cardiovascular health.