I give several B12 injections a day as a community nurse and it is rare to have a bad reaction however this sounds definitely like an adverse reaction and if someone reported this I would not give any more until it had been checked by the GP. There is a yellow card warning system for medications and this would need reported on that. Occasionally it can be the batch that is the problem.
The difference between Wealth Tax, Inheritance Tax and Income Tax
Retiring and living frugally in money from downsizing after years of stress


