Or a potassium deficiency. I have B12 deficiency but I did not have muscle cramps as a symptom, not to say its not one just not one I experienced. But I take a fluid pill and it makes my legs cramp because it depletes my potassium.
Cramping is more likely caused by a magnesium or calcium deficiency. General tiredness and cloudy mental functioning can be caused by low iron and B12. If you're not confident that you're recieving enough vitamins and minerals through your diet you can visit your local health food store. Smaller, family owned ones are your best bet. Most workers are very passionate about health and wellness and can offer a wealth of knowledge. Hope this helps..Well wishes to you!!
You deficient in potassium. Eat bananas or get potassium supplements.