Yes, a complex. The problem could be the dicalcium diphospate added to most of supplements. Inhibits the very uptake of vit B but also minerals like magnesium. NOW food has a good liquid B12 that I could tolerate in small amounts. This was at a time when even brewers yeast caused the symptoms.
I did of course suspect Iodine to be the reason for the palpitations. But found out I could take a load of it without problems. Dosages of iodine; a dropper full or two of Lugols 5 % every other day.