I've noticed being tired and low on energy all the time even doing my regular chores by more than a week.Some other sings I have observed are : shortness of breath, increased thirst, indigestion, brittle nails but I am not sure about the relevance of these. I took mecobalamin 1500 tablets for three days when my body felt healthy and energised. I am not taking it from two days and my symptoms are back. My regular BP levels are usually 65-75/82-92mmHg, pulses 85-90 and I'm 40 kg at age of 20.