There are certain serious diseases where B12 may be elevated.

Kidney failure is one (only some people with kidney disease show elevated levels). Some cancers also. But it is not common.
I have seen mention of intestinal overgrowth of some bacteria as a cause too, but that is not common either.

I am so sorry this is happening to you. Please consider going to the ER today, and getting some emergency feedings or IVs, and help.

Kmeb,
I'm worried about you...I agree with Mrs. D...please go to the ER. Update us when you can. Take care, Liz