If you were anemic at the time you started B12, increased cell formation of blood cells, can cause a temporary decrease in potassium. This can be felt as tiredness and/or cramping of muscles.

However, it is a brief period, of time, and does not continue once the red cell count normalizes. B12 is used by all the body's tissues, and will go where needed.

There are people who have mental symptoms when methylation is not working properly in the body.
Here is an article about it:
http://www.alternativementalhealth.c...es/walshMP.htm

This one discusses methylation also and explains pyroluria, which also causes anxiety. (low B6 and zinc).
http://jdmoyer.com/2011/09/03/b-vita...s-complicated/