Always good to have a reason I have also had this happen when my folate was low , it may be worth you getting it checked I had self inject my B12 every 4 weeks for the last 20+ (cannot really remember how long accurately), and 2 months ago got a similar 'electric shock tingling' all over my body - head, face, arms, hands, legs, feet etc within a couple of minutes of injecting, which lasted about 3 seconds or so
Good sources of magnesium include green leafy vegetables, whole grains, and nuts
Mol Nutr Food Res 2015;59:1364-1372
Keep the injections in a dry place to avoid damage by moisture
And products with food dyes, like candy, gelatin, and certain breakfast cereals, might turn your urine green or blue
What Is Vitamin B12 Injection Used For