B12 THRIVE Why Do I Feel Worse After My B12 Injection? Understanding Post Injecti Oxford Origins B12 Injections: What's the Buzz? Vitamin B12 is the star of several essential functions in the body. However, it's common to be deficient in B12 and as a consequence experience fatigue, Vitamin B12 deficiency, sometimes called cobalamin deficiency, happens when your body is either not getting enough or not absorbing enough vitamin B12 from the foods you eat. Vitamin B12 is an important