I was taking Jarrow 5000mcg Methyl B12 daily, and after about maybe a month of doing so developed shortness of breath (that was occasionally severe) and tachycardia.

I'd like to continue taking B12, though, and I've been told I should try Hydroxocobalamin or Adenosylcobalamin. Would anyone here recommend one form over the other?

I've been suffering from pectoralis/shoulder pain for 1.5 years now that the doctors couldn't seem to diagnose, and I discovered by accident that megadosing on the Jarrow B12 took my pain away COMPLETELY. It's very confusing - I don't know if that means the pain is being CAUSED by a B12 deficiency or what's going on. But because it made me feel basically 100% better, I'm desperate to continue with it! Alas, I have to breathe, and Jarrow's B12 made me feel like I was honestly suffocating at times.