B12 Injection When Is It Worth It and What Can You Feel After One Dose? LondonMassage4U Curious about B12 shots? The Wellness Center Feeling constantly tired, foggy, or run down? Vitamin B12 plays a key role in energy production and nervous system health and low levels can lead to fatigue, brain fog, and weakness. Why Do I Feel Worse After My B12 Injection: 6 Body Reactions Heres why a Vitamin B12 shot is a game changer: more energy, better focus, improved mood, stronger immunity, faster metabolism & healthier hair skin nails. , Whether youre feeling run down, Feeling exhausted, run down, foggy or low this winter? Cold weather, darker days and busy schedules can drain your energy fast and that's where a B12 injection can make all the difference