Howdy everyone.. Went undiagnosed with B12 deficiency for over 10 years. Started on Folic Acid and B12 ( cyano and methyl )... After 3 days the startup symptoms got crazy, to the point of me feeling like my throat was closing up and I was going to pass out. Another side effect was crazy head pressure all over my head and crazy sinus pressure. The head pressure didn't hurt, it just felt strange. This went away after a day and I was able to take my first deep breath in 10 years. Unfortunately this crazy death feeling came back within the next few days. I figured out it was from a huge increase in histamine levels. I believe the b12 startup alone was creating large amounts of histamine PLUS I was eating SPINACH by the handful to raise my potassium. Spinach and Bananas have high histamine content. Soooo... I went to the store and bought some L-Methonine to lower my histamine. The head pressure started dissipating immediately and I started feeling normal again. I just wanted to share that if you don't have the money to buy L-Methonine, it can be found in high quantity in egg whites. Anyways, thanks for all the info I found on this board regarding b12 deficiency. My hands no longer shake, I can breathe easy again, no more numbing appendages and I feel my brain returning back to normal instead of being in DUHHHHH mode.