I have been having palpitations on and off all year, resting heart rate is always over 100..I also could not get my depression under control, the meds that usually worked were not working. I had my b12 level checked and it was too low so had an injection. I found that my heart rate slowed and my depression meds started working. That was 8 weeks ago..I was due to have another injection and forgot to get it..I began feeling ill about 10 days ago, heart rate high again..so instead of just getting the b12 shot I had my level checked to see if the symptoms were because it had become low again...when I got the results they were lower than the first time...so at last I have a concrete reason as to why I was feeling unwell..so from now on I have to have b12 shot every 6 weeks but will also have blood tests to keep an eye on it. If you look b12 up the symptoms I describe are listed, but no dr knew about them that I saw...I know many people suffer with palipitations and hope that this could help others..cant tell you how relieved I am that I know at least one reason why I felt so unwell...and also increased gabapentin and pain is under control again..so hoping for a christmas where I feel a little better. Hope this helps someone.