Has anyone felt worse after a vitamin B12 injection?

[millmoo]

Has anyone had a vitamin b12 injection and felt absolutely rubbish after it?
I had the injection on Saturday and the lady did say that it would take a few days to work but I’ve felt rubbish ever since. Low mood, lack of energy- sleepy! I don’t know if this is just a coincidence as I’m having a hormonal mood swing (no period as have coil) or whether it just hasn’t worked for me?
any advice anyone?

I've never had an injection make me feel worse, but if you're badly deficient in B12 it can take a while, plus the whole loading dose of injections (3 per week for 2 weeks), before you start to feel better

Have you added a potassium supplement?

B12 is known to very drastically increase need for potassium in the short term, and if you don't add/increase potassium intake, B12 can make you really unwell, to the point where it can be outright dangerous.