The Neelakantan 2018 paper showed strong oral absorption in cell uptake (Caco-2) assays, which is why most research community use is by mouth instead of by injection
Common Mistakes to Avoid Most self-injection problems trace back to a small handful of avoidable errors
61:104-108 Masayuki Ikeda, Makoto Asai, Takahiro Moriya, Masami Sagara, Shojiro Inou, Shigenobu Shibata, Methylcobalamin amplifies melatonin-induced circadian phase shifts by facilitation of melatonin synthesis in the rat pineal gland, Brain Research, Volume 795, Issues 12, 8 June 1998, Pages 98-104, ISSN 0006-8993, Carmen Wheatley Cobalamin in inflammation III glutathionylcobalamin and methylcobalamin/adenosylcobalamin coenzymes: the sword in the stone
If you have heart palpitations because of chronic (long-term) anxiety disorders, theres hope