Taking Vitamin B12? Read this first. While B12 is often hailed as a safe energy and brain booster, many real users are reporting unexpected side effects including anxiety, insomnia, Why Do I Feel Worse After My B12 Injection? Causes & Management Bolt Pharmacy Vitamin B12 Injections: Boost Energy & Support Weight Loss Why Do I Feel Worse After My B12 Injection When I first got the B12 shot, I was really surprised what a difference it made in my energy levels. And thats exactly what happens if youre deficient in this essential vitamin. , B12 is involved in Feeling worse after starting B12 : r B12_Deficiency