The signs of B 12 deficiency may be different from person to person. But here are some of the symptoms that have shown to be most frequent: short breath, felling dizzy; pale skin (especially lips and eyelids), mouth soreness, cold feet, cold hands (bad circulation), pain in chests, and heart beat irregularities.
It all happens because the body is not able to produce enough red blood cells and thus there is no enough oxygen needed to normal functioning. Related to this, there is also a condition known as vitamin B12 deficiency anemia, often accompanied with symptoms like nausea and vomiting; weight loss and lack of appetite; disorders like diarrhea or constipation, or even enlarged liver, which is rather a severe condition.
There are also symptoms related to the nervous system. This should never be ignored for it could cause a nerve damaging that can be permanent. These symptoms are: numbness (feet and hands); confusion, a lack of concentration; problems with walking; problems with memory, irritability and/or depression; mania, insomnia, anxiety and other neurological disorders; swallowing difficulties; felling lightheaded or experiencing frequent and/or severe headaches; feeling tired and weak.
Sometimes it can all go without any symptoms, so it would be good for you to do occasional checks just to be sure that everything is all right. You should check your red blood cells and hemoglobin levels.
Even though the cases of vitamin B12 deficiency are not that frequently seen, it is still good to know basic things on the subject, especially if you are a vegetarian. If you follow the vegetarian regime you are probably aware that you need additional sources of vitamins. In that case you can find a solution in vitamin supplements. Just make sure to consult the doctor about the right vitamin supplements.