B 12 injection lasts for 48 to 72 hours in the body.
Liquid vitamin B12 is good for normal red blood cells and it is more effective in nutrient absorption and plays a vital role in keeping lethargy and fatigue at bay.
It makes you happy or uplifts your mood because vitamin B12 is needed for the production of serotonin. Serotonin is a hormone that stabalises mood in people who are deficient in the hormone.
It is a serious condition you need to consult a doctor immediately. You might feel extremely fatigued along with anemia.