Hi. I got my last B12 injection on the 6th February. I didn't feel so bright after it...this happened at least once before. Why is this? Anyway, I put on a 5000mcg patch two days later which did help a bit. This past Monday 19th Feb things still weren't as good as it had been prior to getting the injection so I put on another 5000mcg patch. That evening I got very tired and haven't been well since with sometimes rapid pulse and aches. I am slowly getting better but I have spent long times in bed. Please can anyone help me to understand why this has happened. I read that it's basically impossible to overdose on B12. The patches were working so well. Especially the 1000mcg. Now I am scared to ever use them again. 😣 forgot to say that my arms started prickling and my skin over my body felt as if it had been in very hot water. Aches and pains too.