Increased vitamin B12 levels are uncommon. Usually excess vitamin B12 is removed in the urine. But disorders that affect the levels of vitamin B12 in the blood can lead to too much vitamin B12. These disorders include:
Liver disease (such as cirrhosis or hepatitis)
Myeloproliferative disorders (for example, myelocytic leukemia)
There is a very low toxicity related to taking too much B12, it's more than likey that taking too much will not cause any harm, but like stated above, if you have another disorder going on (you may not be aware of) then you best get to a good doc to help you figure out what if anything eles might be causing you issues.
It's important to take enough vitamin B12 daily for those who have low levels (I started with shots and was weaned onto 1200mcg tabs and this has worked well for me).
From my experiance and understanding, tingling/numbness is due to lack of B12, not too much B12, it's the onset of permanant nerve damage which is why B12 is required in order to reverse the oncomming damage.
My bum is broken....there's a big crack down the middle of it! LOL :)